In reply to the problem experienced in this thread, I too am experiencing the same problem. Running 365 in a local environment. 3048 and the lockfiles don't close on closing the database. I am running the 32 bit version of Office 365. So the problem is not confined to the 64 bit version.
To delete the lockfiles without restarting the computer: Scroll down in task manager until the MSAccess.exe is found and close the application. The lockfiles can then be deleted.
This does not solve the problem, but at least the database can be restarted and the problem reincountered.
Background information: The problem came out of the blue upon which I deinstalled and reinstalled office, to no avail. Microsoft stated that this bug had been fixed with an earlier release of 365. Evidently not!
My question: can I return to an earlier version of 365 and how to do this?
Hopefully Microsoft will come up with a solution soonest.
Thank you.