[SOLVED] Plex Playback Errors on Samsung Tizen 9 After Synology NAS Rebuild — Certificate Chain Fix (November 3, 2026)

Affected Devices: Samsung M8 32-inch Smart Monitor and Samsung QN85C 85-inch QLED TV

Server: Synology DS224+ | DSM 7.4.1 | Plex Media Server 1.43.5.11079 Status: RESOLVED — Secure HTTPS playback restored on both devices.

User uploaded image

About the Author

Alex | Houston, Texas, USA

Military & Intelligence Background

• U.S. Army / National Security Agency (NSA) - Signals Intelligence (SIGINT) Analyst / Cryptanalyst

Civilian Information Technology Career

• Senior Systems Administrator

• Network Engineer

• Network Architecture & Infrastructure Engineering

I'm sharing this firsthand technical investigation because the problem initially appeared to be a Samsung Plex client compatibility issue after a NAS rebuild. After multiple controlled tests and TLS certificate diagnostics, I was able to identify and correct the certificate-chain problem without reinstalling Plex or making changes to Synology's system certificates.

Part 1 — Problem, Workaround, and Resolution

1. The Problem

Following a complete rebuild of my Synology DS224+ NAS, including a fresh installation of DSM and Plex Media Server, the native Plex for Samsung applications on both my Samsung M8 Smart Monitor and Samsung 85-inch QLED TV stopped playing movies. Both devices had played Plex content successfully before the NAS rebuild. After the rebuild:

• Plex launched normally on both Samsung devices.

• Media libraries, movie titles, artwork, and descriptions loaded.

• I could browse and select movies.

• Attempting to play or resume a movie resulted in a playback error.

• The Samsung Plex application displayed an error dialog that required acknowledgment using OK.

PLAYER_ERROR_CONNECTION_FAILED

Playback error occurred.

Reason: BufferingTimeout

Player took too long buffering, stopping playback

The problem affected both Samsung devices, suggesting a shared server-side or connection related issue rather than a hardware failure.

Updating my iPhone and Apple TV software did not resolve playback through the native Samsung Plex applications.

2. Initial Workaround — Allowing Insecure Connections

While troubleshooting, I changed two settings inside the Samsung Plex application. Plex for Samsung → Settings → Advanced

Original settings:

Allow Insecure Connections: Same Network

Prefer Insecure Connections: Same Network

Changed to:

Allow Insecure Connections: Always

Prefer Insecure Connections: Always

Result: Movie playback started working.

This suggested that the playback failure involved the connection between the Samsung Plex client and Plex Media Server rather than the movie files themselves.

3. Isolating the Setting That Made the Difference After the initial success, I wanted to determine whether both changes were necessary. I enabled verbose logging and the on-screen log display inside the Samsung Plex applications so I could observe errors during playback.

I also enabled temporary diagnostic logging on Plex Media Server and forwarded the Samsung client logs to the server.

After repeated tests on both Samsung devices, I found that only one setting needed to be changed.

Working temporary configuration:

Allow Insecure Connections: Always

Prefer Insecure Connections: Same Network

Playback succeeded with this combination.

When I returned Allow Insecure Connections to Same Network, playback failed again. Changing that setting back to Always restored playback.

This established that the Prefer setting did not need to remain on Always. An Important Observation

Although the workaround initially seemed completely successful, I noticed inconsistent playback immediately after making connection-setting changes.

For example:

1. I attempted to resume a movie, and playback succeeded.

2. I attempted another playback, and received an error.

3. I retried, and received another playback error.

4. A subsequent attempt finally worked.

I also compared Resume with Play from Beginning.

This inconsistent behavior was important because changing the setting to Always did not guarantee immediate playback success.

What the Logs Revealed

The Samsung logs showed failed playback attempts using an encrypted HTTPS connection: https://s192-168-1-189.012a11aff27c4f2abf8fe24f73128fbb.plex.direct:32400/ Those attempts generated:

PLAYER_ERROR_CONNECTION_FAILED

BufferingTimeout

Successful playback attempts used local HTTP:

http://192.168.1.189:32400/

For example, during one test on November 3:

Time	Event	Result
3:03:06 PM	Allow Insecure Connections changed to Always	Setting changed
3:03:12 PM	HTTPS playback attempted	Failed
3:03:18 PM	HTTPS playback retried	Failed
3:03:26 PM	Local HTTP playback attempted	Successful

This suggested that Plex was still selecting a problematic HTTPS connection after the setting changed, before eventually switching to working HTTP.

That observation prompted the investigation into TLS certificate validation. 4. Root Cause — Plex HTTPS Certificate Chain Reviewing the Plex Media Server logs revealed repeated TLS handshake errors:

CERT: incomplete TLS handshake

tlsv1 alert unknown ca

The Samsung M8, identified by its local IP address 192.168.1.101, generated multiple certificate-related errors.

Using OpenSSL on the Synology NAS, I inspected the certificate Plex was presenting. The original certificate chain was:

Plex wildcard certificate

Let's Encrypt YR2

ISRG Root YR

Certificate verification failed:

Verify return code: 20

(unable to get local issuer certificate)

The server was presenting a certificate chain that the local OpenSSL installation could not validate against its trusted certificate authorities.

This aligned closely with the failed HTTPS playback behavior on the Samsung clients. 5. Successful Resolution

I backed up Plex's cached certificate, stopped Plex Media Server, renamed the original certificate, and restarted Plex.

Plex automatically generated a replacement certificate bundle:

cert-v2.p12

The replacement certificate chain was:

Plex wildcard certificate

Let's Encrypt YR1

Cross-signed ISRG Root YR

ISRG Root X1

After regeneration:

Verify return code: 0 (ok)

I then restored both Samsung Plex applications to their original connection settings:

Allow Insecure Connections: Same Network

Prefer Insecure Connections: Same Network

Result: Both Samsung devices successfully played movies again.

The Samsung QLED's logs also confirmed that the actual video file was being delivered over HTTPS using TLS, rather than falling back to unencrypted HTTP.

The detailed repair procedure is documented below.

Part 2 — System Information and Repair Procedure

6. Hardware and Software Environment

Plex Media Server

Component	Configuration
NAS	Synology DS224+
DSM	7.4.1-90080 Update 1
Plex Media Server	1.43.5.11079
Plex Web	4.162.1
Subscription	Monthly Plex Pass
Installation	Native Synology DSM package

Architecture	x86_64
Server IP	192.168.1.189
Port	TCP 32400
Plex installation data	Volume 2

Plex Server Network Configuration

Setting	Value
IP protocols	IPv4 and IPv6
Secure Connections	Preferred
Preferred Network Interface	Ethernet 0, manually selected
Strict TLS Configuration	Of
Enable Local Network Discovery (GDM)	Enabled
LAN Networks	192.168.1.0/24
Treat WAN IP as LAN Bandwidth	Enabled, as reported
Enable Relay	Enabled, as reported
Webhooks	Enabled, as reported

Samsung M8 Smart Monitor

Specification	Value
Device	Samsung M8 32-inch 4K Smart Monitor
Model code	LS32FM803UNXZA
Firmware version	1320
Detailed firmware	T-PTMMFWWC-0090-1320.4
Additional build identifier	E95 92200, BT-S (as transcribed)
Application	Plex for Samsung
Plex client version	Initially reported as 5.9.4.1 (exact formatting unverified)
Platform version	9
LAN IP	192.168.1.101

Samsung QN85C QLED Television

Specification	Value
Device	Samsung QN85C 85-inch QLED / Neo QLED 4K TV
Model code	QN85CDFXZA (as reported)
Firmware version	2220

Detailed firmware	T-PTMCAKUC-0090-2220.4
Additional build identifier	A071020000, B T-S (as transcribed)
Application	Plex for Samsung
Plex client version	5.94.9
Platform version	9
LAN IP	192.168.1.252

Samsung QLED Plex video settings during troubleshooting:

Allow Direct Play: Enabled

Allow Direct Stream: Enabled

Maximum H.264 Level: 5.1

Disable Bitrate Limiting: Unselected

No video codec or Direct Play configuration change was required to resolve the issue.

7. Enabling Diagnostic Logging

Plex Media Server

In Plex Web:

1. Open Settings.

2. Select the Plex Media Server in the sidebar.

3. Navigate to General.

4. Enable diagnostic logging and, if necessary for troubleshooting, Verbose Logging. 5. Save changes.

Verbose logging was enabled temporarily during this investigation.

To download the logs:

Settings → Manage → Troubleshooting → Download Logs

Samsung Plex Clients

On each Samsung device:

1. Open Plex for Samsung.

2. Navigate to Settings → Advanced.

3. Enable verbose application logging.

4. Enable Log to Media Server if available.

5. Enable the on-screen console log overlay.

The on-screen log overlay was particularly useful because it displayed application activity and errors during playback.

It allowed me to observe error messages in real time while changing connection settings and testing Resume versus Play from Beginning.

Forwarding the client logs to Plex Media Server enabled correlation between Samsung AVPlay errors and server-side TLS failures.

Important: Disable verbose logging and the on-screen overlay after completing diagnostics.

8. Inspecting the Original Plex Certificate All commands below were executed through an SSH terminal using Termius. The NAS was accessible at:

192.168.1.189

Step 1 — Inspect the Certificate Presented by Plex

Original result:

depth=1 C = US, O = Let's Encrypt, CN = YR2

verify error:num=20:unable to get local issuer certificate depth=0 CN = *.012a11aff27c4f2abf8fe24f73128fbb.plex.direct issuer=C = US, O = Let's Encrypt, CN = YR2

Verification error: unable to get local issuer certificate

Verify return code: 20 (unable to get local issuer certificate) Step 2 — Display the Served Certificate Chain

openssl s_client -connect 192.168.1.189:32400 -showcerts </dev/null 2>&1 | grep -E '^[[:space:]]*[0-9]+ s:|^[[:space:]]*i:|Verify return code:'

Original output:

0 s:CN = *.012a11aff27c4f2abf8fe24f73128fbb.plex.direct

i:C = US, O = Let's Encrypt, CN = YR2

1 s:C = US, O = Let's Encrypt, CN = YR2

i:C = US, O = ISRG, CN = Root YR

Verify return code: 20 (unable to get local issuer certificate)

Step 3 — Verify Using the Plex Hostname

This hostname is specific to my Plex server. Other users must use their own plex.direct hostname.

openssl s_client -connect 192.168.1.189:32400 -servername 192-168-1-189.012a11aff27c4f2abf8fe24f73128fbb.plex.direct -verify_hostname

192-168-1-189.012a11aff27c4f2abf8fe24f73128fbb.plex.direct </dev/null 2>&1

This also returned:

Verify return code: 20 (unable to get local issuer certificate)

The failure persisted even when using the Plex hostname, making a simple hostname mismatch an unlikely explanation for the observed verification failure.

9. Certificate Repair — Step-by-Step

Warning: Back up the original certificate before changing it. These instructions describe the repair performed on my Synology system. Certificate regeneration behavior can vary by Plex version and installation.

This procedure affects Plex's own cached certificate, not the Synology DSM system certificate. Step 1 — Locate the Plex Certificate

My Plex application cache directory was:

/volume2/PlexMediaServer/AppData/Plex Media Server/Cache/

Locate the certificate:

sudo find "/volume2/PlexMediaServer/AppData/Plex Media Server/Cache" -maxdepth 2 -type f \( -iname '*.p12' -o -iname '*.pfx' \) -print 2>/dev/ null

Result:

/volume2/PlexMediaServer/AppData/Plex Media Server/Cache/certificate.p12 Step 2 — Back Up the Original Certificate

sudo cp -p "/volume2/PlexMediaServer/AppData/Plex Media Server/Cache/ certificate.p12" "/volume2/PlexMediaServer/AppData/Plex Media Server/ Cache/certificate.p12.backup-2026-11-03"

Verify the backup:

sudo ls -lh "/volume2/PlexMediaServer/AppData/Plex Media Server/ Cache/"certificate.p12*

Both the original and backup were approximately 3.2 KB.

The original certificate and its backup were preserved with their existing ownership, permissions, and timestamps.

Keep these files private. PKCS#12 certificate bundles may contain private keys. Step 3 — Stop Plex Media Server

On the Synology NAS:

1. Open DSM.

2. Open Package Center.

3. Select Installed.

4. Select Plex Media Server.

5. Click Stop.

6. Confirm Plex has stopped.

This stops Plex only, not the NAS.

Step 4 — Confirm the Plex Process Is Stopped

In Termius:

ps auxww | grep '[P]lex Media Server'

Expected result: No matching Plex Media Server process.

Step 5 — Rename the Original Certificate

Once Plex is stopped:

sudo mv -n "/volume2/PlexMediaServer/AppData/Plex Media Server/Cache/ certificate.p12" "/volume2/PlexMediaServer/AppData/Plex Media Server/ Cache/certificate.p12.old-2026-11-03"

The certificate is renamed, not deleted.

The independent backup remains untouched.

Verify:

sudo ls -lh "/volume2/PlexMediaServer/AppData/Plex Media Server/ Cache/"certificate.p12*

Expected:

certificate.p12.backup-2026-11-03

certificate.p12.old-2026-11-03

The original active certificate.p12 should no longer be present.

Step 6 — Restart Plex Media Server

In DSM:

1. Open Package Center.

2. Select Plex Media Server.

3. Click Run.

4. Confirm its status changes to Running.

5. Open Plex Web.

6. Confirm the libraries are available.

Strict TLS Configuration remained Off during this repair.

Step 7 — Verify the New Certificate

Plex generated a replacement certificate after startup.

Run:

sudo ls -lah "/volume2/PlexMediaServer/AppData/Plex Media Server/ Cache/"*cert*.p12*

Actual result:

certificate.p12.backup-2026-11-03 3.2K

certificate.p12.old-2026-11-03 3.2K

cert-v2.p12 5.9K

The replacement cert-v2.p12 was created on November 3, 2026, at approximately 3:35 PM. Step 8 — Verify the Replacement Certificate Chain

openssl s_client -connect 192.168.1.189:32400 -servername 192-168-1-189.012a11aff27c4f2abf8fe24f73128fbb.plex.direct -verify_hostname

Actual result:

depth=3 C = US, O = Internet Security Research Group, CN = ISRG Root X1 depth=2 C = US, O = ISRG, CN = Root YR

depth=1 C = US, O = Let's Encrypt, CN = YR1

depth=0 CN = *.012a11aff27c4f2abf8fe24f73128fbb.plex.direct

0 s:CN = *.012a11aff27c4f2abf8fe24f73128fbb.plex.direct

i:C = US, O = Let's Encrypt, CN = YR1

1 s:C = US, O = Let's Encrypt, CN = YR1

i:C = US, O = ISRG, CN = Root YR

2 s:C = US, O = ISRG, CN = Root YR

i:C = US, O = Internet Security Research Group, CN = ISRG Root X1

Verify return code: 0 (ok)

SUCCESS.

The new certificate chain validated successfully.

The additional cross-signed certificate provided a trusted path to ISRG Root X1 in this environment.

Step 9 — Preserve a Rollback Option

The original certificate remains available as:

certificate.p12.backup-2026-11-03

certificate.p12.old-2026-11-03

If the replacement causes a serious compatibility problem, the original can be restored after stopping Plex.

First, preserve the new certificate:

sudo mv -n "/volume2/PlexMediaServer/AppData/Plex Media Server/Cache/cert v2.p12" "/volume2/PlexMediaServer/AppData/Plex Media Server/Cache/cert v2.p12.rollback-preserved-2026-11-03"

Then restore the saved original:

sudo cp -p "/volume2/PlexMediaServer/AppData/Plex Media Server/Cache/ certificate.p12.backup-2026-11-03" "/volume2/PlexMediaServer/AppData/Plex Media Server/Cache/certificate.p12"

Restart Plex through DSM Package Center and verify its operation.

Note: This rollback procedure was not required or performed during my successful repair. It would restore the original certificate, including its known trust-chain limitation.

10. Final Samsung Playback Verification

After the certificate regeneration, I restored both Samsung Plex clients to their original settings. Plex for Samsung → Settings → Advanced

Allow Insecure Connections: Same Network

Prefer Insecure Connections: Same Network

Manual server configuration fields remained blank.

Samsung M8 Results

• Secure server connections succeeded.

• Movie playback initialized and completed buffering.

• The player reached the playing state.

• The earlier TLS certificate rejection and buffering failures were absent from the corresponding post-repair test interval.

Samsung QLED Results

I initially verified playback using the temporary workaround.

I then changed Allow Insecure Connections back to Same Network.

Playback continued working.

The QLED's server logs showed:

206 GET /library/parts/.../file.mp4

TLS

HTTP 206 Partial Content is normal for video streaming using byte-range requests. The server explicitly recorded TLS, confirming that the video file was delivered using an encrypted connection.

Before and After

Verification	Before Repair	After Repair
Certificate issuer	Let's Encrypt YR2	Let's Encrypt YR1
Certificate chain verification	Error 20	0 (ok)
M8 playback	Failed with original settings	Working

QLED playback	Failed with original settings	Working
QLED HTTPS video transfer	Failed during testing	Confirmed successful
Allow Insecure Connections	Always workaround	Same Network
Prefer Insecure Connections	Same Network	Same Network
Plex reinstall	Not required	Not required
DSM certificate modification	Not required	Not required

The results strongly support the original Plex certificate trust chain as the underlying cause of the secure playback failures in this environment.

11. Post-Repair Cleanup

Once successful playback was confirmed:

1. Disable Verbose Logging on Plex Media Server.

2. Return Samsung Plex client logging to its normal level.

3. Disable the on-screen console log overlay on both Samsung devices. 4. Disable Log to Media Server unless further diagnostics are needed.

5. Retain the diagnostic ZIP archives privately.

6. Keep the original certificate backup and renamed original certificate.

7. Leave the replacement cert-v2.p12 in place.

8. Keep both Samsung clients on the working Same Network connection preferences. There is no need to leave the clients configured to prefer or universally allow insecure connections once secure playback has been restored successfully.

12. Final Conclusion

This initially appeared to be a compatibility issue involving Plex Media Server, Samsung's Tizen Plex application, or the Synology NAS rebuild.

The investigation revealed something more specific.

The original Plex certificate chain could not be validated against the available trusted certificate authorities.

The Samsung Plex clients could browse library information but encountered failures when attempting to play video over HTTPS.

Temporarily setting Allow Insecure Connections to Always permitted HTTP playback, helping isolate the issue to secure connection handling.

Further logging exposed certificate errors, including:

tlsv1 alert unknown ca

Verify return code: 20

(unable to get local issuer certificate)

After backing up and renaming Plex's cached certificate, restarting the server resulted in a new cert-v2.p12 certificate bundle with a valid trust chain.

Verify return code: 0 (ok)

Both Samsung devices subsequently played movies using their original connection preferences.

Encrypted HTTPS video delivery was independently verified on the QLED. Resolution date: November 3, 2026.

I hope this documented case saves other Plex users from unnecessary reinstalls, network changes, transcoding experiments, or leaving insecure connections enabled indefinitely. — Alex

Houston, Texas, USA

U.S. Army / NSA Signals Intelligence Analyst / Cryptanalyst

Senior Systems Administrator | Network Engineer | Network Architecture

Original topic:

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