Okay, we tested the Finwing again after fixing the GPS. The goal is to test the performance of the fly-by-wire mode, that is supposed to assist the stabilization of the drone.
Right after switching to fly-by-wire mode, it was inverted, and goes to a nose dive. Manual control was toggled, and a high G pull saved the drone from kissing the ground.
Why it happens? Misconfigured fly-by-wire mode that aggregates the roll instead of stabilize it. But the drone, as the cliché goes, will live to fly another day.
Code deployed is APM:Plane 3.1.0-release