Motos Pseudo-Overheating?

Hi,
Our robot is having problems with motors appearing to “overheat” and stopping in the middle of our driver control period. The problem is that they are not warm at all; they just stop working. In some cases they twitch don’t generate any movement.

Details:
We are using 12 motors on our robot: 10 speed and 2 torque.
6 motors are used on our drive train, 4 on our lift and 2 on our claw.
We have our 2 claw motors (torque) y-cabled and run through a power expander; two sets of y-cabled drive train (4 speed motors) also running through the power expander battery. Everything else (lift and back two drive motors) is on the main cortex battery. Each side of our lift is also y-cabled (4 speed motors). This amounts to 5 y-cables total.

I have attached a picture of our motor port setup. We have tried to balance out the circuits on the cortex to avoid overburdening any portion of the board. If we are wrong on this please let us know!

Things We Have Tried:
Newer 7V batteries
New back-up battery
New cortex (in case our battery connections were worn or lose)
New motor controllers
Replacing the gears inside motors (to reduce any friction)
Slew rate code (for drive train motors)
Getting rid of Integrated Encoder Modules (We tried these for a day for some PID code and removed them the next day - robot randomly power cycled and had similar issues. Upon removing the IEMs we resolved these issues).

Nothing we have tried has helped. Robot works great when motors all function, but is completely crippled without all motors working. Our team is at a loss on how to fix this. We have state on Saturday and any help would be appreciated!

Thanks!
motor setup.PNG