I tried all of the violent and software “solved!” “remedies” to no avail. Finally I bit the bullet and disassembled the phone and replaced the camera. The only tough part is getting the cement off the display. However, my re-assembly was faulty and I lost the function of the down Vol button. Now I have to use the up Vol button to get the on-screen slider, and use that. Also, you need the down Vol button for screen shots, but there are several free apps that put a screen shot soft button on your home screen, or use the Home button to make screen shots. My camera replacement has worked fine for about seventeen months now. I installed Item name: 3-L-234 0TO(em) “OEM Back Main Rear Camera Cam Module Parts For LG G6 G5 G4 V10 V30[LG G5 +Tools]” from E-1 Products Inc. on eBay.

El hierro (4th post up) has the answer; see my comment. The cable which might be to blame is illustrated at https://www.diymobilerepair.com/lg-g5-led-flash-laser-auto-focus-cable-replacement