Copter flipped in stabilize for no apparent reason


I’m trying to make a small 230 mm quadcopter fly with an mini APM v3.1 from Banggood, running APM:copter 3.2.1.
I struggled to reduce the vibration levels and now I ended having a very decent behavior in stabilize mode.

But yesterday I was out to do some tests, and when I wanted to land, and during the (slow) the copter flipped upside down at 1 m height. No damage but I’m surprised it happened this way.

I join the .log and .bin (cannot figure out which one is useful). The flip occurred at the very end of the flight. Any clue of what could cause it?

Ho, forget it! I went flying today and one motor did not spin normally. One of the motor wires soldering was broken. Problem solved!