"OK so my issue is "where do you go to see if your ESC/Motor combo is Pixhawk safe" ? Should be simpler then this.
Round 1: Afro 30A ESCs and sunnysky 3508s 700Kv motors -> no go
Round 2: Flash ESCs... better, damaged one of the ESCs during flashing…"

"Check your compassmot values. If they are NULL, change the to 0. You could be running an old firmware or mission planner which had an issue with compassmot not setting the values properly.."

"That's what I had to do. Reformating worked for only for a short while. I swaped SD Cards, and mine has been working since.

Happy flying."

"Re-format your SDCard...Doesn't hurt to try."

"Don't panic, no cause for alarm if your platform is stable.  Just good to know if something weird happens."

"I can't guarantee anything but it solved issues for me. Try first reformatting your current card. If you have another sdcard lying around, try it out. I know 3DR also had to change their initial shipments of Pixhawks due to bad (or slow) sdcards.…"

"I'll just put in my 2 cents worth probably not related. I've had problems with Pixhawk not booting up properly due to a bad or slow sdcard. Maybe the logs stopped recording because of that? I agree though, there was a reboot sequence."

"1) Try re-formatting your MicroSD card.
2) If you have done a compassmot, check for NAN values in your parameters under compassmot X Y Z, set them to '0'."

"I know it's a late reply but I would go with the 180, given you have them both."

"Jeffrey,
   I had the same problem for the longest time, and as Andrew mentions below, make sure to use the RC7&8 outputs (490 hz) from the same row as the engine output, not the analog (A0 - A12) side outputs (50hz). 

You might also want to ramp…"