Blew up controller, same way as before, sus about the whole setup.

[apprisco]

Hi all!

I built my own electric scooter(yes, not a bike, I get that.)
It's a 72v 7000w total (3500w per motor beast)
but I'm running slightly weaker controllers at 3000w each.
I wired them up to a single battery pack at 72v 100A bms in parallel.
However, the ESC for the front motor keeps on blowing up.

I wired this in a way that allows me to use individual control of the motors, so I can choose to run the front wheel or the rear wheel.
Is this possibly the reason why the front ESC is just blowing up all the time?
Or is there another reason? Could the XT90 cable / extension cable be faulty?
Any ideas at all are appreciated, thank you so much.

 

[apprisco]

It's possible that the rear ESC would've also blew if I had it powered on, but luckily a motor cable's crimp had fallen off, so I didn't actually connect that motor, and had the rear ESC powered off during the whole incident. (still connected to the battery pack)

To sum up the situation, scooter was riding fine, stopped at a traffic light, died. Did not try to accelerate again before the ESC blew.

Additionally, the behavior rn is funky:
Plug in "blown up" front ESC: massive sparks in the xt90 connectors (likely pointing to a short) and prevents even the rear ESC from powering on (smart bms!)

Unplug blown up esc: no issues, scooter works fine with rear ESC.

I'm seriously confused as to how this happened, and why it happened twice. Each one of these ESCs are 90$ or more, and the damage is quite serious so I don't think I can even repair it.