I believe I found the problem: my pedal had a faulty potentiometer for the right brake, which was causing slight brake commands without my input. I read that in version 1.9 any small movement in the rudder above 290 knots causes the yaw damper to disengage, the aircraft starts to oscillate its wings until it becomes uncontrollable, the autopilot disengages, and the aircraft dives. I bought a new pedal and apparently the problem was solved. Anyway, thank you for your attention.