Benchtop Test of Motors with QGC - Motors run individually but not all at the same time

I have a benchtop test rig to test the motors and ECSs. I tried using the sliders in the QGroundControl. I tested with both PWM and DShot1200. In both of the protocols, motors run individually, but if I try to run all 4 at once using the “All” slider, only one of them runs, not the other three.

Why that might be the case?

I’m using Pixhawk 4. QGC v4.1.4. PX4 v1.12.0

I have a similar issue where the relevant channels are connected to Servos and Esc. But only the Esc runs in all the channels even though it is connected to channel 5 ( fixed wing case - ) !!