Same problem, but not only on lock screen
Since 5 days I have my G3 (855 Modell). I was happy the first two days, then I discovered the problem, that the device is always unlocking itself, when in my front pocket. It's because of the Knock on feature. I deactivated this now.
But since yesterday i have the same issue: three times, i was unable to unlock my phone. The touchscreen simply did not respond. I had to remove battery. Today, I read this post and tried the firmware update of the touch, but I have the impression it did not change something in the version.
After this, today I had again once time the non responding touch while unlocking and shortly after, I had the issue after ending a phone call! The touch did no longer respond and had to remove the battery again!
I hope this is not a hardware issue, otherwise I will hurry up to the seller to exchange the phone, because its only 5 days old.