For many months (probably more than a year at an absolute minimum), I have had a four finger double tap gesture (to display a custom context menu) that has worked with no problems at all. Very recently (but exactly when, hard to say), this has broken somehow. I can change the track pad gesture to something else (say, four finger swipe down) and the context menu appears, and I can assign some other action to four finger double tap (like display screen shot dialog). I just can't get the context menu to show up with four finger double tap anymore, like tapping with four fingers repeatedly. Nothing happens. I assume this is just another problem that somehow only I in the world have, and that nothing can or will be done to fix it, but it's really annoying because I've been using this constantly until now.
(Note that I don't know when it broke, because it was several days prior and I assumed a system restart would fix it, which I didn't do until today, and it did not improve the situation.)