I'm still on Yosemite; so can't test. Does it work if you press the esc key?
Same problem under Yosemite. esc doesn't work.
- It works fine with 6.2, El Captain so if you want you can upgrade to 6.2 however there are a lot of other issues with 6.2.
- I believe the best thing to do will be to use the ESC key.
Works OK for me either pressing F or esc. Have you recently updated OSX? Did you trash the prefs? It's usually necessary to clean up what’s left behind after updating OSX.
Start by quitting Lightroom 6.
Launch Finder and click the Go menu whilst holding down the Option (alt) key. Then go to Library >> Preferences and clear everything relating to LR6 which usually means deleting the following files:
Then re-launch Lightroom.
The Library is hidden under the Go menu in Finder until the Optn (Alt) key is pressed.