Well great…
While Plexamp 3.0.0 and at least some later versions worked again and did not show the cumbersome issue, where on EVERY start the UI is blank until you delete the settings folder, Plexamp 3.1.0 reintroduces that issue.
Well done… not!
Plexamp|440x656
EDIT: Sorry, this is on Windows 10 1909
This is the bug: