Ok I've figured out the Bluetooth
Just like the WiFi the problem is a poor connection to the bottom board which is free to float around. It was an Idiot who designed this connection, bottom board should have been sitting on plastic shelf or spacers.
I've attached two pictures showing the pin 1 that needs to contact the conductive plate 2.
I fixed by placing small stacks of the screen adhesive under the four corners of the floating bottom board 2.
This forces it up to make a better connection with top board 1.
Obviously you need to remove screen to do this.
However, it may be possible to fix by jamming a small rigid piece of plastic in the top of micro usb slot above the jack as that's the corner of top board that needs to be forced down.
Another alternative maybe to open the corner from the back and try and force the bottom board against the top. There's two screws and some prying to do there.
Also, in addition to the adhesive spacers, I suggest placing some copper tape on the conductive square (2) to improve reliability of the connection. Similarly with the wifi squares which are on opposite side and corner of floating bottom board (2) to the bluetooth square.
My Bluetooth and wifi are now fixed. Yay.