I have never had this problem before, but 3 times in the past 2 days when I filter a dozen or so images by star and color ratings and then press F to view them full screen, there was no way to get back to the regular view, whether pressing F again or even trying Alt-V to bring the View Menu up and trying to get back to the regular view. The problem may have something to do with hitting Esc inadvertently, but I had to Ctrl-Alt-Del to get the task manager and close LR. I'm on a 64-bit Windows 10 computer.
Anyone else experience this?