Most probably some cloude service or anything other. Why it is not possible to disable it through 'Window' dropdown, I don't know. All I know that i have to work and a white, unclosable box is keeping me from doing it.
Try this... Start PS. The Press Ctrl +k (shortcut key for preferences), Select Performance.
Change the state of the "Use Graphics Processor" (If it's checked, then uncheck it.. Select OK
Now restart PS and see if the box appears. I don't know if this will help you, but it's a place to start to troubleshoot what is occurring.