Potential Fix!
On my late 2015 27" iMac.
Disabling Smart Zoom (double tap with two fingers) in Trackpad settings and I'm now feeling like it's fixed. I did a restart of the machine also, so perhaps throw that in as well, though I cannot honestly remember if I changed my settings before or after the restart. I had been trying to get a few tasks done and was going crazy with the issue.
I had also reverted my cursor size and color at the same time in Accessibility settings, so possibly also important.
I really, really hope this works for everyone! And I'm so sorry if I've gotten your hopes up if it doesn't. I know the feeling. It seems to be working normally as it always did.
Also, an issue where after hitting Cmd-Cntrl-Q to lock the screen, and then hitting Esc to quickly put the screen to sleep wasn't working, i.e., hitting Esc after the screen was locked didn't do anything until several seconds after it was locked, also started behaving normally again. Now, hitting Esc after Cmd-Cntrl-Q immediately puts the screen to sleep.
I had felt that while the tap to click issue persisted that it was a conflict where the system just wasn't sure what it was supposed to do/had conflicting actions it thought it should take and just ignored the tap. It just had this weird feel to it. My cursor also jumped around quite often upon tapping, usually moving a few centimeters away from where it was.
Again, hope I'm not giving out false hope to anyone! Good luck!
Edit: Yes! Also fixed the very frustrating pinch to zoom issue, which is also very important for my work!