Copter3.4-dev Crash (EKF_CHECK-2)

I had a weird crash with my big camera X8 using 3.4-dev.
I had 4x 20min flights without any problem using 3.4-dev before. I used it because I needed the external Barometer…
I flew it in stabilize while suddenly it rolled to the left and crashed (EKF_CHECK-2 error appeared). The Logfile is attached…

Does no one have an idea what could have caused this crash?!

Hiya, looks like the same problem as people are having with 3.4 on the pixracer: