Why is my bluetooth range so poor?

So recently I decided to replace the screen on my iPhone 6s plus. While researching parts, I decided also to re-shell the device, placing the internals from the original housing into a new home. The phone worked beautifully (or so I thought) for several hours and continues, even now, to function perfectly for everything (GPS, wifi, screen, battery) aside from bluetooth connectivity to headphones, speakers, my Apple Watch, etc.

The bluetooth signal is so poor (about 3 feet) — that my Series 1 Apple Watch is now essentially useless and my array of bluetooth headphones are also now ornaments only. What in the world is wrong with my bluetooth?

I have already replaced the wifi/bluetooth ribbon antenna (the curvy one) as well as replaced the grounding bracket and the NFC bracket. I am out of ideas for how to fix the issue. Any ideas?