Thanks for replying.
Of course I tried that FIRST. It did not work.
If it is a Windows problem, why no other file manager is affected then?
But no worries. I found what was the issue and the fix. The culprit is a setting for a new feature in Directory Opus 13 which needs to be disabled. I discovered it a few hours after I posted my question.
To fix this glitch, go to…
Settings, Preferences, File Operations, Copying Files:
Under "Show icons overlays for files being copied"
DISABLE: "Show ghost files for queued copies"
And that’s it. No more problem.