There is an ongoing issue where iCal don't sync with Exchange/Office365.
The problem is on the Exchange server side and they are (hopefully) doing something about it.
https://discussions.apple.com/thread/7514805
https://community.office365.com/en-us/f/153/t/437730
Looks like this:

The problem is on the Exchange server side and they are (hopefully) doing something about it.
https://discussions.apple.com/thread/7514805
https://community.office365.com/en-us/f/153/t/437730
Looks like this:

Last edited: