Outlook 365 Desktop stopps refreshing calendar view of shared calendars

At one of my colleagues outlook does not update the calendar of other users anymore, not even in the scheduling assistant.
I have tried the following:

• Outlook in cached mode, cache file recreated.
• Cached mode deactivated
• shared calendars re-shared
• recreated windows profile

Outlook web shows the appointments of the other users.
I was able to fix the problem by reinstalling office 365. however, after a few days the problem reoccurs.
How can I get Outlook to show the appointments permanently?