Recently I have build test 4rotor with this configuration:
DJ F450 frame (with DJI ESC, props and motors)
Pixhawk 3 PRO kit (ublox m8n GPS) stable branch
I have successful tested indoor position mode (with LPE and px4flow fusion), copter has perfect stability without any drift.
But outdoor flight resulted in crash (I have LPE with only GPS fusion): after short period of time (position mode) copter starts to drift rapidly until crash.
Sorry, if it is some stupid misconfiguration, but for now I have no ideas what cased the crash. I only see that GPS estimated position is not correct, and Pitch angle is opposite to RC control (I tried to stabilize copter before kill switch was engaged).