Any experience with mRobotics Pixhawk?

I just purchased 2 original Pixhawks from mRobotics and installed them in two DJI F550 hexacopters. I flashed them with the latest stable version of the P4 stack. I have been trying to make them operational, but they seem very unstable. For example, when I power them up, the progress bar in QGC moves across very slowly and finally it times out. At this point it tells me that it was unable to retrieve the full set of parameters from the Pixhawk. Occasionally I can get it to initialize properly.

I also am getting erratic behavior from the GPS, where it locks and unlocks in rapid succession every few seconds. I am using the mRo PixHawk GPS M8N + (LIS3MDL + IST8310), which was recommended by them as a solid unit.

I have discussed these issues with them, so they stepped me thru a totally new install of Mission Planner and Ardupilot to test the hardware. Everything was working OK in this scenario. The system booted fast and the GPS lock was solid.

So I went back to QGC and re-flashed the P4 software. When I boot up with the USB cable attached, it works OK. But when I remove the USB cable and power up for a flight, the same thing is happening as before, and I get a timeout when it tries to boot up. And the GPS is still very unstable, locking and unlocking every few seconds.

I suspect there is a software compatiility issue with P4 and the mRo Pixhawk. Or maybe QGC has something to do with it? Right now I’m not operational and have some time-critical missions I have to fly.

Can anyone give me any feedback about using the mRo Pixhawk and their GPS with P4? And is there some known software bug that might be causing this problem?