Plex has stopped working properly since upgrading to macOS Sierra

1. I start up Plex Media Server on my Mac Mini (16GB ram, plenty of drive space) running macOS Sierra.
2. Works fine for awhile, then becomes non-responsive (other apps, websurfing, etc, are fine)
3. I click on the PMS icon in the top Bar and chose quit. It goes away (visually anyway)
4. I click to start up PMS and promptly receive the message - The application "Plex Media Server" is not open anymore.
5. I check in the OS X Activity Monitor and fine 3 entries for Plex Media Scanner running.... close them.
6. Try starting PMS again and IMMEDIATELY get the same message -The application "Plex Media Server" is not open anymore.

No other obvious instances of Plex anything showing up in the activity monitor.

I am forced to restart the entire system before I can get Plex running again and then its a repeat of above.

I DID do the latest updates the last time... no change.

HELP!