i am having the exact same problem, i can see headers in notification bar but once i enter outlook mail is not there. uninstalled and reinstalled i get on email and then it goes back to not seeing mail in inbox.
when it was working i used to get a message that outlook has been processing data for a long time and there is an overheating warning.
i am using a new (less than 6 months) one plus 5+ my outlook is an exchange enterprise company version of outlook.
can anybody help? so frustrating