same here, mine was the GPS connector.

One of the connectors of my flex cable had become damaged somehow, it was scratched on the square metal side and broke off and stayed on the motherboard when removing the flex cable.

After replacing the flex Cable, Phone is like new!

The iPhone 6 with this fix and a new battery, which was almost as easy to replace as any phone just with with a few special tools, is ending up being the phone I had hoped, the first one to really not need an immediate upgrade for maybe 3-4 years. I was HATING it for the last year since the battery, which ended up at 74% of original capacity, stopped it from working properly, no thanks for your added “help” apple, how about some truth. It had been essentially useless, but now its everything I need and will hold me over till some other hopefully 3-4 year phone has my name on it. I think next generation will be more ideal.

WARNING: Reattaching the antenna cable was the most difficult part for me, it took about 5 minutes of trying to get it to pop back on, everything else was easy.