Gmail account problem

Hi, my Galaxy A17 5G has been working fine until a couple of days ago.

I have two email accounts set up on the phone; one is a BT Internet account, the other is a Gmail account. 

When using the Gmail app, I used to be able to see the two different accounts and choose which one I wanted to use. 

Now, the Gmail account is not showing, I can only use the BT Internet account to send and receive emails.

If I go into settings and Manage Accounts, it shows both accounts. I have deleted the Gmail account and reinstalled but no joy. My Gmail account works perfectly well on my PC. This problem has only occurred in the last week. I've done all the usual stuff like clear cache, restart and all the other suggestions on YouTube but nothing works. 

Frustrating to say the least.