How can I diagnose if my LG G2 screen is defective?
As far as I can tell, the problem is that the LCD is getting interference from the antenna.

To fix it, place some tape in between the white antenna cable and the circuit board. Basically, on the bottom, there are 2 parts that snap on, and then there is another square that is left "floating around". This has to be flat the same orientation as the LCD. Place the tape above it so it insulates it from the white cable that should be passing above it.