wasted a few hours ‘bughunting’ … I just forgot to use pull up resistors on the I2C bus 
short explanation idea/experiment :
this (allready joined @home) mobile device transmits, after the push of a button, 3 single bytes packets (with some interval time)
1 on SF 7
1 on SF 9
1 on SF 12
@home I will have a dedicated RPI with an application that responds when received one (or more) of these packets.
The device responds by sending then it’s location from GPS (when there’s a sat lock)
The application receives the coordinates and calculates the distance(s) between the gateway(s) that received the signal and the device location.
The application (mini server) sends the calculated distance / RSSI / SNR back to the device where its displayed.
so basically its a handheld mapper 
without the need of a phone when it works I can think of ‘automatic / continue modes’ nice thing is that the data is immediate available @home
with some fantasy , a faster processor/more memory and a programmable attenuator/compass you can use it to find gateways ? 