Weird crash in RTL after Geofence Violation

I built a motorized glider and have flown it more than 30 times with a total of about 10 flying hours without having any serious problem. As far as I could see the glider behaved perfectly in all flying modes. However, the last flight ended in a disaster. After a geofence violation during thermal mode, the plane was flipped over and dived into ground. Any attempt to return to manual mode was denied and at the end, the plane was broken into pieces after heavy fluttering of the wings

The log file can be downloaded from

Any help to find the reason of this crash is appreciated.

Best regards