Tilt Rotor, Quadplane with two front tilting and sudden pitch in forward transition

Hi community, I am building a quad plane with front two motors tilting and rear two motors fixed. while I am doing the transition from Qstablise to FBWA, the plane pitches so hard and turns upside down, stalls and fall back to earth. had some expensive crashes. I found that back two motors are not switching off immediately after transition they continue to produce lift which is creating forward pitch. I am not aware of parameters which i can change to switch them off immediately after the transition.

Are you sure you are switching into FBWA and not manual?

Have you got a log?

Yes, I am sure I was using fbwa mode. I will attach log by tomorrow.