FYI -
I had many problems with backing up.
Kept getting notifications saying Drive Folder could not be found, maximum storage reached (when it wasn't), invalid credentials, authentication errors and connecting to server errors.
I disabled and reconfigured through Avast's web portal and on app, as well as uninstalled multiple times.
What seemed to have worked for me is turning off Google's 2-Step Verification. I think for me (and possibly others), there is some type of connection issue when having Google's 2-Step verification enabled, probably due-to the inability of Avast to constantly connect freely without verification.
After turning that off 2-Step, I:
-disabled GDrive through Avast's web portal
-uninstalled and reinstalled app
-reconfigured everything.
Haven't had a notice or error since.
