I should add that I'm running on MacBook Pro, OS X 10.12.3, with two displays.

This is not a show-stopped, but sure can be annoying. In that case, Command-Q to end LR is my only recourse. Moving the mouse pointer to the top of the screen reveals the LR menu, but not the LR window top edge (that contains the 3 little circles).

When it's not stuck I can move the mouse to the top of the screen, and the LR menu and LR window top edge comes back in view and I can click on the 3rd little circle to exit full screen mode. The F and shift-F keys work fine for what they do, but if I make the LR window full screen (on the Mac) by clicking on the 3rd little (green) circle at the top left corner of the LR window, then it can get stuck in full screen mode, but not always. I've discovered different full screen modes in LR tho. disable the option and of click in accepting.

there you will find the option of Disabling optimizations of complete screen. will locate the file of the executable one of Team. It's been almost 3 years since George started this thread, and I'm having the same problem with LR CC in 2017 (my release is labeled 2015.9 in the About box). Team don't have this configuration option, but you must try with these steps.

How to escape full screen mode pc