What is triggering the EKF_CHECK error and subsequent crash?

I am using Copter 3.4.0-rc0 on a coax copter frame. I am planning on upgrading my firmware to 3.4.4-rc1 before flying again, but I am not sure what I am seeing is a firmware or sensors issue. Basically, I recieved EKF_CHECK-2/0 three times. The third time my copter flips over and turns into an earth seeking missile. I reviewed the logs and it doesn’t seem to be a vibe issue, but both the Gyro and Mag values go AWOL right before crashing. Not sure if this is the trigger or just a symptom of the trigger.

I have attached the log file if anyone is interested. Thanks!

28.log (3.2 MB)