Have you tried rebooting after you changed the drive letters?
That probably means you have either created a system-wide hotkey on that key within Opus (Settings > Customize Toolbars > Keys), or you've floated the Operations toolbar (so the toolbar itself is a separate window, not connected to a lister or file display; that will make any hotkeys in the toolbar global).
Are you running Opus elevated ("Run as Administrator")? It'll say "ADMINISTRATOR" in the titlebar if you are. That could explain things, as the admin context can have a different set of drive letters to the standard user.
That's the wrong type of log file. (Looks like either a summary of some kind, with counts of events per process but without any individual events, or something saved from a Task Manager type tool rather than Process Monitor.)
It looks like there are mapped network drives under the old letters, but we need to work out why Opus is showing them and Explorer isn't. Once we know that, we should be able to filter them out in the same way.
We'll change Opus to ignore these, but if you expand that Network branch in regedit and delete the empty B, D, F and S keys there (only leaving the Z key which has something in it), then reboot, the unwanted drive letters should go away.
Since they are empty, they won't be doing anything and are safe to remove.
(Why something has created those empty keys in the registry, or failed to clean them up properly when removing them in the past, I am not sure.)