During throttle up, motor speed is dropping down after seconds of running

Hi. I’'m new here and I would like to ask on my issue with my drone below. My drone type is quadrator. I’m using PX4 version 5 for my Flight Controller and I’m monitoring my Flight Log using Mission Planner.

The issue is that, motors cannot maintain rotation at 1900-2000RPM range (ideal take off speed) during initial throttle up whereby after few seconds, motor 1, 2 and 3 RPM drop drastically more than 10% decrement.
It was observed that after 7-8 seconds running time, motors are slowing down and not maintaining at desired speed.

Motor 1: Speed reduction to 1622 from 1855 RPM (-12 %)
Motor 2: Speed reduction to 1702 RPM from 1903 RPM (-10.56 %)
Motor 3: Speed reduction to 1145 RPM from 1822 RPM (37.16 %)
Motor 4: Speed maintains at 1944 RPM from 1944 RPM (by right, this condition should be the ideal case).

I already checked on hardware and it seems that no issues at all , motor, ESC, FC, power distribution board etc. are ok based on the troubleshooting. I checked then on my Dataflash Log, I can see the signal from FC to ESC are not right. You can refer RCout parameter from my attachment for reference.
I just want to ask here, what could be the potential problem related to this unbalance signal to the ESC? as I can feel that something is not right with the signal to all 4 motors. Hope all get my points .TQ in advance.