Before posting screenshots, I found something that could help you pinpoint the problem. The way panels are arranged seems to have something to do with it.
Panels config that gives me the error:
LEFT SIDEBAR
- panel splitter
- thumbnail browser
- navigator
- artist picture
- album cover
I dont get the error popup if I place the navigator panel above the thumbnail browser.
Looks like the navigator panel doesn’t like moving up and down depending if the node I choose needs the thumbnail browser or not. The radio node makes the thumbnail browser disappearforcing the navigator panel to move up to take its place. If I click on a playlist in the navigator panel, the thumbnail browser panel reappear forcing the navigator panel to move back down and that’s when the error popup appears.