I use MP 1.3.49
Test all motors in sequence did not work for me, Pixhawk 2.4.8 I just upgraded to Copter 3.5.1 from 3.3.3. Quad X
Also I struggled to start all 4 motors simultan after ESC calib, only 2 motors will start with Throttle 30%.
After i adjusted parameter MOT_SPIN_ARM to 0,2 and MOT_SPIN_MIN to 0,3 i was able to start all 4 at Throttle 15% ?