Alright, here is a schematic I just put together due to a lot of these parts being thrown together because this is all made out of spare modules I had. As for debugging only one motor and motor driver is connected.
PWM is at 2.5 KHz. You reminded me of a few other tests I had done a week back, I had also tried driving it at much lower PWM speeds, all the way down to 10 hertz, the current 3.3V is temporary as had been tested with similar results at 8+ volts, just with more crashing and concerns.
XT60 connector as seen in the picture does not mean this is being driven from a battery, was just installed out of convenience.
Motors peak out at 1.8A and while running with a bit of a load pull 0.8A at 3.3V.
With the flyback diode installed voltage rails still appear stable all the way up to 8+ volts.
I am aware that internal charge current on the MOSFET's field may be quite large and if you think that is the issue I will just move on to using a much better motor driver I had plans for a while now as compared to just putting something to drive the MOSFET as there is a lot of other issues and features id want in a newer one as these cheap motors are just temporary as well as a lot of the other prototyping things. Just wanted to try and get this version working.
Any issues regarding the microcontroller's firmware have been worked out and operates perfectly fine as long as it's not connected to the MOSFETs. Due to this I am very certain it's a current or overvoltage on the gate signal. It seems weird that it would become increasing more unstable at higher voltages if it was an issue regarding the gate pin making me thing that there must be flyback leakage reaching the gate pin or driving the ground signal a bit too high, despite that I've tried a lot of filtering with some of the best capacitors I have with no improvement at all making me lost as to where the issue is. Another issue that may point to an issue on the ground line (I may have failed to measure on the oscilloscope due to it being grounded to it as well) was that I was noticing the USB interface was more likely to go down when under this load than the radio. These cheap microcontroller board I have been using have proven to have an unstable USB connection in the first place.