Networking/Wifi : One UI 9.0 causing Mobile Data Loss

Oh my goodness! I am having the same issue! I genuinely have no idea what to do!

Both the UI9 and Oct security updates have broken several features, including wi-fi calling while on airplane mode.

Seems 9.0 update is worse then 8.5 update

Hi all,

Quick update, I called Samsung Technical Support and they suggested to do some troubleshootings. I have not tried these steps, so I just copied paste what I got from them.

I. First check steps

Clear the Phone's Cache Partition

Residual networking code left behind by the OS upgrade can jam the 5G modem driver.
1. Power down your S24.
2. Plug it into a computer via a USB-C data cable.
3. Hold down the Volume Up and Power buttons together until the Samsung logo pops up.
4. Use the volume rocker to move down to Wipe cache partition and select it using the Power button.
5. Confirm Yes, and then select Reboot system now

II. Enable Data Roaming Globally

An odd quirk in the new UI layout causes the system to flag localized 5G towers as "foreign infrastructure," dropping the data stream unless roaming permissions are turned on.
1. Go to Settings > Connections > Mobile networks.
2. Toggle Data Roaming ON.

III. Wipe the "SIM Toolkit" App Cache

The phone uses an internal system app called "SIM Toolkit" (or Smartcard Service) to push carrier-specific configurations to the new UI framework. If this data is corrupted, 5G traffic stalls.
1. Open Settings and go to Apps.
2. Tap the Filter and sort icon (next to "Your apps") and toggle on Show system apps, then tap OK.
3. Search for SIM Toolkit (it might also be named Smartcard Service or have your carrier's name).
4. Tap Storage, then tap Clear Cache and Clear Data.

IV. Manually Rewrite the APN Type Protocol

Sometimes the Access Point Name (APN) resets to default, but the authentication protocol remains wrong for 5G routing. You can manually force the phone to accept all internet protocols:
1. Go to Settings > Connections > Mobile networks > Access Point Names.
2. Tap on your active carrier's APN profile to edit it.
3. Scroll down to APN protocol and change it to IPv4/IPv6.
4. Scroll to APN roaming protocol and change it to IPv4/IPv6.
5. Scroll to APN type and ensure it says default,supl (if it is blank or only says default, type in ,supl exactly without spaces).
6. Tap the three dots in the top right corner and choose Save


I do not know what are the impacts due to these troubleshooting steps and these steps are fully quoted from the Samsung Technical Support. So, I'm not responsible for any errors if it occurs to your phone.

I just wanted to share what I got from them. Hope this helps