For me it's been such a frustrating experience with the door lock sensor only working maybe every 5th time. I believe I've tried it all. I even found something buried in the manual about "3 touches to lock" and that still only works every few times I exit. I read the fob should be 28-40 inches away (check), the fob and your phone/digital key shouldn't both be in your bag together (check), don't grab the handle (check), brush the sensor (check), try a different finger (check), wait at least 3 seconds after door close (check), touch the sensor gently for up to 3 seconds (check). It's the entire reason I found this whole forum, because I was googling for at least the third time how to lock my doors with the touch sensor.
It is ABSURD to me that it's this difficult or that "user error" is this easy or common for LOCKING THE DOOR. My GT had the button instead of the sensor and it never once failed, ever. If there's something on this list of "tricks" (which SHOULD NOT NEED TO BE A THING) that I haven't tried please please enlighten me.