Apple - Why is the Force Touch "taptic" TrackPad not clicking/selecting on 2015 MacBook Pro?

My trackpad (MBP Early 2015) was working, but there was no haptic feedback, or any indication that force touch was working. Other functions (trackpad, single tap, scrolling, etc.) were working. Here's what my settings looked like:

For me, it was fixed somehow by an SMC reset with the charger disconnected, while powered on. Basically, I pressed Control + Shift + Option + Power button. The system instantly shut down without warning. Force touch and haptic feedback were back when the system turned on.

_{Do I recommend this? No. It's an unclean shutdown. Did it work? Yes it did.}

Got this this weekend, I was starting to go a little cranky when I saw my 2015 MBP wouldn't click. Tried restarting, to no avail.

At one point, I unchecked 'tap to click', big mistake because I couldn't click anymore, so I connected a USB mouse to regain tap-to-click, but still no trackpad clicking.

I came across this answer from user jbjose80 on Discussions.Apple, recommending instead of rebooting, to shut down and boot back up. Sounded silly, but worked like a charm. Phew!

(Originally posted on Retina MacBook Pro (non-Force touch) trackpad can't "click" as usual, but that was the wrong model)

Same problem, but the SMC reset (Control + Option + Shift + power button) fixed it.