I think this issue has been flagged before and was maybe supposed to have been fixed by an update, but that is not my experience. We have 3 family gmail accounts that download into our local computer Thunderbird app (Windows 10). 2 of these accounts function normally, but since 24 Sep one account shows the error 'Unable to write the email to the mailbox. Make sure the file system allows write privileges and you have enough disk space to copy the mailbox.' No emails have downloaded from gmail for that account since that date. The computer disk is less than half full, so it should not be a space issue. As far as I can see all accounts are set up identically with all system permissions, notably write, showing 'allow'.

How do I resolve this issue ?