Yes, my problem solely concerns Theater Mode. I wasn't sure whether or not to call it a plugin or skin. I've seen both. Now I know! Thanks.
Skins change the appearance of MB by changing various colors and sometime the elements of the layout.
Plugins add additional functionality to MB.
Theatre Modes provide a different way of viewing MB.
For the most part, one has nothing to do with the other. The lone exception is that Theatre Modes need the Theatre Mode plugin in order to work.
I don't want to side-track the thread but your comment made me curious. Is there some advantage to this? Perhaps you're thinking Windows caused my problem. If so then I'm sorry to say that I'm the most likely culprit. I was handling other issues and this problem was likely an unintended consequence.
I just noticed that you're using the store version. Get the Portable (or even the Installer) version and stop using the Store version.
First off, the Store version doesn't get updated nearly as often as Portable or Installer. Secondly, the Store version basically runs under the control of Windows, and as such doesn't always work as expected. Understand that I'm not saying your issue is because of the Store version, but it's certainly possible. And the only way to know is to try one of the other versions.
A big advantage to using the Portable is that it's, errr, portable. If you're replacing your hard drive or your PC, you can simply copy the entire directory in which MB lives to a thumb drive or some other storage space, change the hardware, and copy MB back from the 'backup' storage to the new hardware and you're up and running.
I strongly suggest the Portable version. Get it from the downloads page of the website, or from the first forum topic. Once you have it "installed" download the latest patch version and apply it per the instructions in my signature below. Make sure to place the Portable version in it's own directory. If you only have one drive letter (C:\) then create a new directory C:\MusicBee and put it there. Update to the latest patch, get the Theatre Mode in question and see where you wind up.