Drop in Torque With High Motor Count

I am part of a VexU team and I am building the 24inch robot. we currently have 14 motors on the robot but started to feel that the drive motors (actually all of them) were putting out less torque than they did when we only had some of the subsystems plugged in.

We started digging into it using the brain onboard diagnostics. We found that with all the motors plugged in, the stall torque would be .6 NM for a single motor (we tested multiple motors). When we unplugged most of the motors from the brain, the stall torque of a single motor jumped up to 1.2NM! Double what we could get before and we simply unplugged nonactivated motors from the brain.
The stats for these motors online says that the stall torque is over 2.0 NM which we have never been able to achieve.

I was hoping for comments to see if other high school or VexU teams have experienced a similar issue so that we can hopefully nail down if this is a fixable issue and what it is caused by. We have looked into the limitations of the battery and the brain to see if that was the problem but it seems to us that we are well within the limitations of the battery and we cant figure out what would be limiting the motor output torque. I will probably also post this in official technical support with further detail in the near future but wanted to get your guys’ opinion first

Thanks,

Fusion Robotics

Jason