Found this fix after I flashed a custom rom & lost my knock on feature. Hope it helps you guys, I didnt realise how much I used it till it didnt work.
How to access hidden menu on LG G2
3845#*802# (for International model)
3845#*801# (for T-Mobile)
3845#*800# (for AT&T)
5689#*980# – (for Sprint )
Dial: ##228378 + send (Verizon)
Other models, please use 3845#*YOUR-MODEL-NUMBER#
Dial 3845#*802# > setting > update touch firmware
Notes, the 802 to your LG G2 Model Number.
The guide shows a few more tests to do, bu I only used the "update touch firmware" step & it now works better than whenI had stock rom, seems more responsive.
Dont think its been posted but please feel free to remove or whatever if it has, just hoping to help peeps out, as this place has always sorted everything for me in the past on various devices.
I did not figure this out myself, I cant post the source as I need 10 posts 1st, so will do when I can, but the site is mylgphones dot com.