Some possible reasons:
The script uses a dll or COM dll in that folder. Cannot be unlocked.
The script uses a dll or COM function that locks some files in the folder or the folder. QM cannot unlock.
The script itself opens and does not close a file handle. Only the script can unlock (close).
Bugs somewhere.
And many other reasons, I don't know or remember.
Only the code that locked the file can unlock it. Or programs like Unlocker.
QM always closes files when finishes using. Now I don't remember other cases, except dlls and file triggers, when QM uses a file or directory handle for a long time.
The script uses a dll or COM dll in that folder. Cannot be unlocked.
The script uses a dll or COM function that locks some files in the folder or the folder. QM cannot unlock.
The script itself opens and does not close a file handle. Only the script can unlock (close).
Bugs somewhere.
And many other reasons, I don't know or remember.
Only the code that locked the file can unlock it. Or programs like Unlocker.
QM always closes files when finishes using. Now I don't remember other cases, except dlls and file triggers, when QM uses a file or directory handle for a long time.