This issue is usually due to the configuration of the resource account (room mailbox) in Office 365 / Exchange which adds the meeting organizers name to the subject hence it being displayed doubled.
To address this we suggest running the following command in PowerShell / Exchange Management Shell.
Set-CalendarProcessing room1@domain.com -AddOrganizerToSubject $False -DeleteSubject $FalseNote! Replace
room1@domain.com with the equivalent of your resource account (room mailbox).