[FrankJ]

In the case of breaking linkages, I suspect one motor was broken & not turning, wired so the motors were turning the in opposite directions, or the linkage was under designed to begin with.

I would think you would be more likely to get balanced torque with one victor feeding the same voltage to both motors, rather two victors with the same PWM signal to different motors. Especially if one gets overloaded & trips the breaker.