Wrong servo outputs on quadcopter using APM

I am using the APM 2.8 in my quadcopter. I initially uploaded the most recent versions of the mission planner available for the APM 2.8 but I faced a problem in calibration. Sometimes compass calibration failed and sometimes the accelerometer calibration. I then found out Mission Planner 1.3.72 which worked in the process of calibration. But the flight was terrible and my quad crashed to a single side. I then checked the servo outputs and they were very different from what it should be. On a level surface and 1/2 of the throttle my servo outputs were:

I don’t know what’s the problem in this as channel 3 is moving much faster than the other. I’ve also checked the transmitter and there is no issue with that. Also, the servo outputs change randomly without a proper sync. Kindly help me in figuring out the issue. Is it a firmware issue or something else?

This is meaningless. A bench test like that tell you nothing useful.
The APM hasn’t been supported in years, suggest you replace it with one that is.

I hadn’t attached the propellers just to see why my first flight failed

That test has no validity.