[dcribbs]

#pragma config(Sensor, S4, , sensorI2CMuxController)

It looks like you are configuring S4 as a Sensor here

#pragma config(Motor, mtr_S4_C1_1, liftRight, tmotorTetrix, openLoop, reversed, encoder)
#pragma config(Motor, mtr_S4_C1_2, frontRight, tmotorTetrix, openLoop)
#pragma config(Motor, mtr_S4_C2_1, backRight, tmotorTetrix, openLoop, encoder)
#pragma config(Motor, mtr_S4_C2_2, dropper, tmotorTetrix, openLoop)
#pragma config(Servo, srvo_S4_C3_1, ploop, tServoStandard)
#pragma config(Servo, srvo_S4_C3_2, servo2, tServoNone)
#pragma config(Servo, srvo_S4_C3_3, servo3, tServoNone)
#pragma config(Servo, srvo_S4_C3_4, servo4, tServoNone)
#pragma config(Servo, srvo_S4_C3_5, servo5, tServoNone)
#pragma config(Servo, srvo_S4_C3_6, servo6, tServoNone)

and here you are trying to use S4 as a motor/servo controller.
I am not sure, but I don't think the S4 port can do both at the same time.