Outlook disconnects on Azure VD

We tried restarting/ rebooting the VD but it seems to not have helped.

We also tried deleting the users profile in Outlook and then add new profile. That doesnt work either. 

Mind you this happens to only one user (or a few) but not everyone...

Outlook locally seems to work just fine, but not Outlook on AVD

What to do next?

Thanks in advance!