I grepped the entire KDE repositories, and nowhere does the string "/mount" appear, so you are either using third party software, or have it stored somewhere in your configuration files. I suggest to look for that string in your home config directories using this Konsole command (can take a long time):

find ~/.[a-z]* -type f -exec grep -H "/mount" {} \;

Is there a way to trace the message back to its originating command? Nothing that I have in autostart in KDE's systemsettings is giving that message.

Also the title of the error message is: Error-Plasma Desktop Shell

So it seems to be kde based.

You likely have a shortcut somewhere from a time when you used something mounted to /mount. Did you try the command from comment #1?

"You likely have a shortcut somewhere from a time when you used something
mounted to /mount."

Where would this shortcut be located? Why would it be launching at startup?

"Did you try the command from comment #1?"

Yes, but I didn't see anything that looked like it would be a startup item. There were a couple hundred lines there from other miscellaneous config files, so I can't be sure though. Doesn't kde have it's startup items consolidated to a single folder or two for me to look?

This sounds quite like a distro problem or configuration problem.

What if you create a new user account and login using that account?

It seems to have stopped doing it after some upgrade.