Programming or Electrical?

[rsegrest]

Ok, here is the setup:

8" mecanums -> Nano Box -> CIM Motor -> Jag -> PWM -> DSC

Programming in C++ using the FRC library (using polar plane)

Problem:
When the robot is up on blocks for testing purposes:

Slow reverse - one set of wheels spins forward [light on jag indicates forward code (light is green)] and one set spins backwards (light is red)
Full-speed reverse - both sets spin backwards

Things we have already tried:
Calibrated jags
Swapped PWMs between ports - same problem occured on other side
Put on new PWMs
Put on different jags
Same problem occurs on different DSC (so both sets of ports on both DSCs would have to be bad if this is the problem)
Changed code to Cartesian plane

Also, when we drive forward all works as expected (lights are green on jags and all wheels spin in the same expected direction)
Could this possibly be a coding issue or are we missing something else?