I have a network tuner I use with Plex so I don't have any experience with that. You could just try removing Plex and reinstalling it from Previous Apps on the Apps page. It should keep your libraries since they are in appdata.

Or, click on Plex icon and select Support to see where that takes you.

I managed to start Plex server by removing the setting "--device=/dev/dvb/" in extra parameter. I'll troubleshoot the tuner card issue another day.

Again, many thanks for your support.