(fixed)
SCH-i545 Same issue, completed my 5th screen replacement on this phone (the previous 4 replacements completed in years past... I've broken this phone and replaced nearly half of the parts in it.)
I tried everything, I mean every single fix I could find including painstakingly removing the rubber seal on the midframe and replacing it with the one from the previously working screen just like David suggested. I tried to put folded up tinfoil in places to make sure everything was completely connected but in the end the solution was that the GPS spring had been slightly impacted (which I guess is easy to do if you press it with your finger or if the board is installed without everything being aligned properly). I used a thin needle and slid it parallel to the surface of the motherboard to get in-between the spring (not a traditional spring, it's more like a loop in the shape of a shoe/boot) which caused the spring to pop back up. Now it properly connects to the GPS antenna on the inside of the rear frame and all is grand.
* There are a total of 6 of these springs on the motherboard (4 small, 2 large for wireless charging) make sure all of them are not impacted/smashed down.
[https://s32.postimg.org/8ke7uadpx/GPS_spring.jpg|GPS Spring]
[https://postimg.org/image/z5gqpug35/|GPS Spring]
Cheers is this helps and sorry for the long read and the time wasted if it didn't!