This issue usually has to do with the configuration for the Room account (resource/room mailbox) in Office 365/Exchange which adds the meeting organizers name to the subject hence it being displayed doubled.
To address the issue please run the following command in PowerShell/Exchange Management Shell:
Set-CalendarProcessing [email protected] -AddOrganizerToSubject $False
Note! Replace "[email protected]" with the equivalent for your Room account in the above command.