Arduplane 3.6 switched to GUIDED after path lost in AUTO?

Sorry for not providing logs (that’s not my plane), but I’ll try to describe issue in precise way.

My fellow showed me one log with strange behavior in AUTO mode. His plane had lost thrust while in AUTO. Motor didn’t stopped but was not enough to keep airspeed and altitude. It decreased target airspeed to ARSPD_FBW_MIN, lost airspeed down to ARSPD_FBW_MIN and then begun to descend (Stall prevention enabled). In one moment (I think it was wind gust) it made sudden dive with roll and pitch beyond limits and plane eventually lost path to WP. And then it unpredictably enters GUIDED mode.

Geofencing was disabled but AFS geofencing was enabled. I suppose such a logic (switch to GUIDED when plane can’t keep mission path) can make sense but I’ve never read about it and can’t find it in code.

Is it a bug or a feature?