Forgive me if this was already discussed, but playing around with the pwm connectors, the wiring diagram says that pwm_3 is connected to E4 which I think associated to heater 4. In any event PWM3 is controlled by turning off Heater 5 (m307 H5...) and control the pwm 3 by calling heater m280 P5...
This is extremely confusing and not intuitive. The wiring diagram for the servo connector says e4, which is H5 to control pwm3.
The error is that it should at least label Heater 5 along with PWM_3. Heater 6 with pwm_4 etc.