I can duplicate the issue here, which appears to be the old R-M-W hardware problem.
I moved the PWMs over to PORTC, and everything works fine.
Since I2C uses pull-ups instead of bi-polar driven outputs, it's more susceptable to R-M-W problems.
If you cannot move pins around on your project, you can get away with the following.
In general, I do not recommend doing this type of modification.
But in your specific case, it should work.
SPWM_PIN LATA, 2, _CH1
SPWM_PIN LATA, 3, _CH2
SPWM_PIN LATA, 4, _CH3
SPWM_PIN LATA, 5, _CH4