Chosen Solution
It was already in bad shape, not able to charge with power below 40-60%, which I figured was due to the charging port and the screen was cracked all over. So I change both and initially it would go as far as loading the OS but then reboot. Gradually it got worse til now I get as far as the T-Mobile splash screen before it reboots. Any ideas? New motherboard in order?
Boot-Looping in the LG G4, G5, V20 are known issues and admitted by LG as a manufacturing defect. This is currently a well known class action lawsuit. I suggest contacting LG to see if they are willing to fix it for free.
