After doing a screen replacement my WiFi range went down to about 12 feet, and Bluetooth connectivity was inexistant. Taking out the logic board I had lost the tiny rubber protection at the top end, and replaced it with a piece of rubber which was too thick. As a result the tiny golden hook did not quite touch the steel frame, which is acting as part of the WiFi, BT and GPS antenna. Having removed my improvised protection strip and replaced it with a thin layer of glue, bent the gold connector out a bit, and re-installed the logicboard 0.5mm further up, I've got back WiFi connection to a mast 500 m away. So it's not just important to screw in tightly the long top screw of the black WiFi Antenna/EMI shield, make sure the little gold hook of the logicboard is in good contact with the steel frame too. I cleaned the steel frame with Isopropyl alcohol too.