Hi @Wimpy. Thanks for looking at Parcellite.
In general, panels have been flakey on my native install test of 18.04 beta 2. Much started when I placed “Weather Report” left of clock and right of Notification/Indicators area of “Traditional”. A typical symptom is lacking audio or network icons and incomplete panels, including blank.
Mate-Tweak switching panels is slow for some reason and slow often means incomplete. It’s not really a slow system.
I eventually did this Live session on this hardware that’s been running 16.04 since day 1. Still is - I’m dual booting 18.04 at the moment.
EDIT: I’ve already ruled out things like Compiz, Marco, nVidia and Nouveau. The Live boot runs Marco and Nouveau.