I have a user who is having trouble with her group email in outlook. She will be able to see her emails just fine on the any browser through the portal.office365.com url. When she uses the outlook desktop app though it will stop syncing her emails after a while. Here's what we have tried so far to fix it:
disabling and re-enabling cached exchange mode. This fixes it temporarily before it stops syncing again after 15 or so minutes.
Repair office suite, both quick repair and online repair.
uninstall office 365 then reinstall
We removed and re-added her account in Outlook
deleting the .ost and .nst files and rebuilding them.
Ran a support tool that can specifically troubleshoot shared mailbox issues. https://support.microsoft.com/en-us/office/about-the-microsoft-support-and-recovery-assistant-e90bb691-c2a7-4697-a94f-88836856c72f?ui=en-us&rs=en-us&ad=us#/ It didn't catch anything of note though we did delete the .nst file again as there was a rule targeting the group inbox.
Had the user sign into a another laptop to see if the problem re-occurred there too. The problem did not follow her on there.
Compared office build version with others in the same group. The version was the same for a couple other user's in this group and they are not having this issue.
Updated office suite to the latest version. Along with making sure Microsoft updates was up-to-date.
A ticket has been created with Microsoft Premier Support. O365 support has stated that since the issue is client only, they will not help us troubleshoot it.
The user's laptop was re-imaged, less then a week passed before the issue re-occurred.
I don't know what our next step should be to fix this. If it helps she is on Version 2104 - 13929.20296