Outlook losing connection

Hi everyone - running into an issue that could use some help with -

Had a user (win 10, 365 desktop, on AD domain) who would become disconnected in Outlook - "need password" - clicking on it would pop up white box but disappear quickly. Only solution was to reboot computer - it would reconnect without issue and work for 2 days and change, only to happen again.

I've done the usual troubleshooting - uninstalled/reinstalled office, new profile, new email pw, ran sara to diagnose (no luck). Ended up setting up user with new computer as was overdue.

Now having same issue at another client, two users. Want to try and resolve without rebuild. One one, I ended up deleting the user account completely, removing the registry tree for that user and recreating - same issue. It's very odd, and hopefully a clue - that it is consistent about failing after 2 days and change.

Anyone seeing this/have thoughts? Thanks in advance!