Jeff, top marks for perseverance sir.
I don't think there's an easy answer to your question. Perhaps one last bit of off the wall digging...
Make sure MC is closed, including the server in the tray if you use that.
Open the registry editor (regedit.exe) observing all of the usual dire warnings associated with registry editing, and head here:
HKEY_CURRENT_USER\Software\JRiver\Media Center 18\Properties
Now look in the right hand window, scroll down and you should see a bunch of entries starting with "Tag Info - Always show..."
As far as I can tell, the one that ends with (1) refers to an "Audio Only" list, which I assume you're working with. Try double clicking that, then check the string, looking for the Album ID field, and if it's there, delete it, along with its, what looks like, tab delimiter.
Save changes, start MC, did that fix it?
I tested this on an existing field, and it did remove that. I don't have an orphan to test with.
-marko.