Pixfalcon x Alien 450 Pitch back during takeoff

I have a Pixfalcon that pitch backwards when trying to launch. The motor direction is correct, the escs are calibrated and the props are correct. So far I’m stuck. The specs are 40amp simon k escs with emax 650 motors. I’ve built a bunch of racing quads and built an APM 2.6 quad without any problems but this is stumping me. I’ve reset the pixfalcon, and went through the calibrations but received the same results. Any help would be appreciated.

in case, any trims in transmitter…?