Additional features, settings, or issues not covered by specific Microsoft Teams categories
I had the issue and managed to solve.
The cause was an employee who had send me an invite for a period that he was on vacation. He marked HIS event to show as out of the office. However, when i accepted it it change my status to be OOO.
See if you have events of other users accepted by you in which you see that they marked the event to display as OOO.