Hmm I think creating a support ticket for this would be my advise(https://support.mendix.com/hc/en-us)
Seems that something might gut stuck
This issue has occurred as the ‘lock’ is not released by studio pro and you are seeing this message even though nobody is committing/updating anything.
So please try to commit/update the changes after some time as lock automatically get releases after some time.
But if the issue still persists after 20 minutes or more, please contact Mendix support or raise a ticket at Mendix support portal.