Lightroom Classic: Watermarks have always exported and now stopped. Works with new watermark one time but not a second won't export.

Probably a preference file issue, Jim. 

A Preference File will survive a Lightroom uninstall/reinstall. Sometimes weird behavior is corrected/cured by resetting the preferences.

Reset Procedure:

1. Close Lightroom.
2. Hold down [Alt/Opt]+[Shift] while restarting Lightroom.
3. Overwrite the Preferences when prompted by the dialog.
4. Close Lightroom.
5. Restart Lightroom.

Does the watermark issue continue after resetting the preferences?

I don't understand what you're trying to do. I have attached a screen shot but don't have a clue what the next step is

You need to click on the actual program icon - not on a desktop shortcut. 

I just checked and realised my Watermark has become really hard to see, as if it had more transparency than before. It works though, on Win 10. You may want to check you watermark settings and test with a different opacity or colour, maybe you just cannot see it any more?

Thank You. I found a way by going into Preferences and clicking on watermarks. You click on each one and click the option to rename and reset it and it worked.  Thanks for your help.  If it happens again, I'll do it your way. It will be quicker