I have exactly the same - overnight sync with Gmail stopped working. Similarly, I have another account on the webd.pl server - I have two different e-mail accounts on this server - the first one works, the second one does not work, it has "mail checking error, incorrect server response."
Sometimes emails from Gmail are successfully downloaded once a day, other attempts fail
Huaway P30Lite, AquaMail (aquamail from google play store, not Huaway AppGallery)