Office 365 Outlook Calendar "No free/busy information could be retrieved"

Recently one of our staff can’t retrieve free/busy information from Outlook. The errors he’s getting when using Outlook’s Scheduling assistant to view free/busy info of meeting attendees.

  1. No free/busy information could be retrieved
  2. your server location could not be determined

When looking at the Calendar properties in Outlook Options he gets “Some permissions cannot be displayed”
His account is being sync’d from our on-prem AD server.

This problem doesn’t happen when using his iPhone

this problem resolved itself. so it will remain a mystery