Weird Free/Busy in Scheduling Assistant issue

Hello, all!

We have encountered a very strange issue with two users' O365 accounts in our ~350-user on-prem Exchange synced to the cloud environment. Both of these users' Free/Busy information is completely blank to other viewers, from a month back of the current date until ~2-3 months in the future. Free/Busy information is viewable from before a month ago, and in the future beyond 2-3 months. This "zone of availability invisibility" is organic, moving forward as time progresses.

A few details:

-Scheduling a meeting to either of these users appears as if they have their availability completely open

-We have changed these users' permissions on their calendar properties to Organization -> Full Details, and the problem still occurs.

-This issue can be reproduced both in Outlook Online and locally-installed Outlook application.

-Happens regardless of Cached Exchange Mode being on or off

-Microsoft Remote Connectivity Analyzer tests all return green

-Viewing either users' availability via the Scheduling Assistant in local Outlook application shows very strange behavior. This will sound weird, but the "zone" I mentioned above can be temporarily shortened by scrolling far left or far right, then clicking "Refresh Availability". This will show an extra ~2 weeks of availability information in the past and future, but disappears again if "Refresh Availability" is clicked again. This behavior can be reproduced by any other end user.

Has this happened to anyone here before? If so, have you found a solution beyond disabling the account and migrating the user to a new one?

-Ry