DOpus 12.9 & 12.9.1 Directory not empty appears occasionally while moving folders

Recently I've had this happen 7-8 times - ever since I upgraded to 12.9.
Upon inspection - all files are moved just fine and it's just the empty folder that remains.
Hitting retry on the dialog does nothing instead of reattempting to move the folder (in this case delete it as it's just empty).

Deleting it manually works but is just more work.
Moving it again works as well.
I am positive no files are created or changed in the folder while it's being moved.

This could have nothing to do with Opus and be related to Malwarebytes locking the files temporarily if it's scanning them while moving but happens too seldom for me to reproduce properly. Also there's no problem with the files being locked as they are moved without a problem. It's just the empty folders that remain.

A peculiar thing is also that it only happens for folders containing video files.
And before you ask I don't have any shell extensions related to video metadata.

I'd look at what's happening using Process Monitor. That should show if something is creating extra files or creating/releasing locks around the folder removal attempt.

If we're talking about a non-Windows NAS then it could be a bug in that as well.

Windows 10 to Windows 10 only. Could be a peculiarity of the new SMB version they enforced with 1803. Can't really monitor with procmon as it doesn't happen that often but I'll try doing it a few times when initiating new move operations and see what I get.

Today after moving several hundred gigabytes more I'm 100% positive this only happens with folders containing video files. Could DOpus be trying to read the video metadata for some reason while moving them? Nothing else makes sense. Either way the files themselves don't give an error. I'll keep procmon running when moving such folders next time and get back if I have any useful info.

The only thing Opus might load while moving a file is the file's icon, which might be triggering a shell extension or antivirus on your system, which maybe takes a while to release the files.

(There have been exploits in video subtitle data, so antivirus may have a legitimate reason to inspect video files when they're opened.)