We have a user in our organization, presumably the only one experiencing this issue. When they use the Outlook Schedule Assistant it shows specific users as unavailable. When this is happening the user is able to view Free/busy times in Outlook on the Web.
When we delete the users in question from the Address Book cache, the problem goes away and we can see free/busy times, for about 10 - 15 days.
This has been happening for about 2 years now, on multiple laptops and different versions of Office. We are currently running 1907.
The user prefers to be in cache mode, I've tried defining Send and Receive groups to include the Address Book, thinking this would resolve the issue for good, but it doesn't.