Stab mode, flying normally, then tumbled

I am a bit of a newb at analyzing logs. I’ve looked through these as best I could for clues and I would appreciate any insight any of you may have into my problem.

I had been flying mostly in Stabilize mode but switching to Alt Hold and Loiter occasionally when I needed to sit the controller down or do something else momentarily. After flying away and back in Stabilize mode for a minute or two, my quad just tumbled. It sounded like it lost power to at least one if not all of the motors but even after it crashed, the Pixhawk was still powered up.

After the crash, I tested all of the motors and ESCs to be sure none had given up on me. All worked but I noticed that a couple of the ESCs seemed to have different calibrations. I plugged each of the ESCs directly into the throttle output of the receiver to test one by one. Two of them seemed to reach peak motor speed at half throttle and the other two reached motor peak much closer to full throttle.

I had properly calibrated the ESCs before and this model has been flying well for a while.