Description of problem:
On serial touchpads (most Lenovos) three-finger taps are often detect as pinch gesture due to the pointer jump the touchpad detects when we go above 2 fingers.

Version-Release number of selected component (if applicable):
libinput 1.6.*

How reproducible:
sudo libinput-debug-events --enable-tap

Then tap with three fingers. That should produce BTN_MIDDLE but you'll find it often detects a fake pointer motion and then switches to a pinch or swipe gesture.

Additional info:
from https://bugzilla.redhat.com/show_bug.cgi?id=1455443