Pixhawk Failing Pre-arming Checks and inconsistent behaviour

Hello, I’m new to the drone building hobby and I’m have a few problems with setting my multi-copter up. My problem started when I began to calibrate the ESCs. Because I’m using a Pixhawk, I heard from Facebook forums, that BLheli D-shot/One-shot 125 ESCs need to be calibrated from the Pixhawk side, using Mission Planner, because you can’t calibrate them using the BLheli suit because the ESCs can’t communicate to the suit through the Pixhawk as it uses some sort of different language to communicate. I proceeded to calibrate them on Mission planner by pressing the calibrate button but nothing happened. I also tried to calibrate the ESCs by doing the all at once calibration method but that too doesn’t work. After another try at doing the calibration on Mission Planner, I kept the USB in connected to the computer and plugged in the battery and then when I pressed the arming button, the motors would make a few musical tones. As I moved the throttle stick about, I noticed that the motors would make some sounds in response and after holding the throttle at 100% the motors actually calibrated. The only thing was, is that they throttle was calibrated upside-down.

The only reason why i was allowed to calibrate on these attempts, was because the Pixhawk decide to cooperate and displayed the Red-Green-Blue sequence, which I believe means ESC calibration is needed and this would be that way as soon as I plug in the USB into the computeessing the armr AND after it requests you unplug and replug it in so it can connect to the MAVlink. But unfortunately, on the majority of other attempts, It would straight away display double-flash Yellow an or after I it has been connected to the MAVlink. I would go onto doing the mandatory set-up for the ESCs but when it comes to pressin the arming button, it would only do the three tones.

This behavior is very inconsistent and I cannot find any explanation or correlation to the drones conditions and its behavior. The only time I have ever gotten close to successfully calibrating the ESCs was after a chance that the Pixhawk would display that certain sequence of behavior.

The Pixhawk has never displayed the solid Green ready to fly status but only the double-flashing yellow and the Red-Green-Blue sequence. It has on one occasion displayed double-flashing Green and on another occasion double-flashing Red. I don’t know what the last teo mean but the Pixhawk seems to do different things. Now whenever the Red-Green-Blue combinatin happens, it doesn’t let me callibrate it still.

The last time I checked by using mission planner, it would audibly talk and it mentions Gps recalibration needed a bad ahrs. I did a compass recalibration or at least tried to in mandatory hardware list but slso when I did the setup wizard.

Here are the main parts I’m using for the quadcopter:
Pixhawk 2.4.8 with latest firmware
30A ESCs racerstar BLheli d-shot/ one-shot125
Radiolink AT9s with Rd9 receiver
Ublox mn8 gps

This is part of a project I’m doing fo my A-Levels so if anyone can help me figure this problem out it would be greatly appreciated.