Hold down the Shift Key when Launching TB to get it in Safe Mode. See if it acts differently. It sounds as if the Profile folder might have become corrupted ... Try backing them up and then creating NEW Profiles to set up the Accounts in, one last time: and see if the settings 'stick' in the new profiles. https://support.mozilla.org/en-US/kb/profiles-where-thunderbird-stores-user-data https://support.mozilla.org/en-US/kb/using-multiple-profiles Did they all just update to Catalina, By the way?

This sounds like the situation where the application hasn't been properly installed. Tim, did you solve your issue??