I have on the 3 drones the following problem:
The GPS connects and disconnects often (when powered via battery) I get the following message:
GPS 0: detected as u-blox at 115200 baud
as a result, the drones cannot navigate by using GPS, and I was experiencing a lot crazy crashes.
If I power the ErleBrain from the Raspberry with the classic power adapter, I do not have this problem. It seems that you have some issues with the power and in particular the UART of the PXFMini.
Indeed, if I connect a usb GPS to the Raspberry, all 3 drones do not have problems and they can fly.
I tried a series of combinations like changing batteries, etc etc etc.
The only solution is to use an usb GPS.