So far I've had this happen twice with customer repairs. I'm still trying to figure out what the issue is but my suspicion is that it's similar to what happened with a few LG G4 repairs--that the new frame itself is causing the poor signal. On the G4 I was able to swap between screen+frame assemblies and go from good to a poor signal, even though I could spot not difference between them, at least as far as the spots on the frame where the motherboard made contact with the frame are concerned--the frame with the poor signal was noticeably thicker.