Access Won't Close

Sometimes when I use MS Access, when I come to close it, it appears to close down normally. However if I then go to reopen it it won't. If I go to Process Explorer it shows that the original MSAccess.exe process is still running and I have to kill it.
This generally happens when I am developing a VBA app that I have. The code is in one .accdb file which is the one I open and the data, through linked tables is in a separate .accdb file.
I've had this app for many years and it has only recently started doing this.
Any ideas what is happening and how to stop it?

Win 11 Pro, Access for MS 365 (Version 2602 Build 16.0.19725.20014) 64 bit.