I’m using the same version and see the same behavior.
There are other threads on the topic, some dating back a year, so you’re not the only one to mention it.
None of the threads I saw mentioned a fix/workaround/etc., so it seems Plex will have to address it in a future update.
Search the forum with fullscreen maximize tags:player-windows or similar terms to see the threads.
Here’s a couple that I found.