This seems to be a revenant. I see this behavior again in version 14.0.4.1982. It usually occurs at first start of PLSQL Developer after booting the system (w/o any autostart stuff involved).

The reproduction scenario differs a bit from my initial description. Currently I start the Developer manually, but using it mostly on my second desktop (Windows 10 Pro 2004, Build 19041.572). I don't know, whether this relates to the faulty behavior.