I noticed that there are more than one threads about this problem so I want to try collecting some information about it and see how many users affected by it. The purpose of this thread and poll is to take the outcome and contact LG and some Tech news websites, making LG respond to this issue ASAP.
If you not sure about having this issue, you can check it as follows (it worked for me) -
1. Open the Dialer and enter 277634#*# to enter the Service Menu.
2. Go to Device Test -> Service Menu - Manual Test -> Touch Draw Test - Manual.
3. Now touch/tap/knock/slide on the test area (all of it) until its almost full and watch for missing registration (you will touch the screen and there will be no red mark). I repeated the test several times and almost every time I had misses.
You can add the device model (H815/H815x/H812/H811/H810/LS991/VS986/US991) and more information in the comments .
I have the international H815 and this issue killing my Knock Code experience (Had the G3 without any issue).
I found a video that demonstrate the issue (it's not my making, but I do have the same issue) .
The app in the video is Multitouch Test and can be download here -
Another video demonstrating the issue (G4 on the left and G3 on the right) -
Another test by coolmaster121
I sent emails to some Tech news websites, here is the first reports (thank you Android Authority and GsmArena!) -
According to Android Police LG US knows about the problem and they're looking into it.
Keep posting your experience and updates until they will issue a fix.