Main 8 Port, no PWM Signal

Hey,
I am currently setting up a new VTOL.
It is very similar to the E-Flight Convergence but can also tilt the rear motor in flight direction. Therefor I just use the Convergence Airframe definition and added a slightly changed mixer definition into the /etc/mixers directory on the Pixhawk. I am using the CUAV V5 Nano flight controller. It has 8 PWM outputs on the main-port, but no aux-port.
The only thing I canged with the mixer file is to replace the “Null Mixer” ( Z: ) with the mixer for my rear motor.

M: 1
S: 1 4 0 -20000 10000 -10000 10000

The mixing for the rear motor works fine, but my left elevon does not move (output 8).
Also in the attached logfile there is no Output 7 logged. (Actuator Outputs Main).

Don’t pay to much attention to the logfile, the PID’s are not tuned yet. Any tips in that regard are appreciated tough.

I also have another question regarding the Yaw Check Bit, what does that mean exactly?

The whole mixer file:

Summary

Adapted E-flite Convergence Tricopter Y-Configuration Mixer

Motors

R: 3y 10000 10000 10000 0

Tilt mechanism servo mixer

#Center up:2000 down:1000
M: 1
S: 1 4 0 -20000 10000 -10000 10000

#RIGHT up:2000 down:1000
M: 2
S: 1 4 0 -20000 10000 -10000 10000
S: 0 2 5000 5000 0 -10000 10000

#LEFT up:1000 down:2000
M: 2
S: 1 4 0 20000 -10000 -10000 10000
S: 0 2 5000 5000 0 -10000 10000

#Elevon mixers

M: 2
S: 1 0 7500 7500 0 -10000 10000
S: 1 1 8000 8000 0 -10000 10000

M: 2
S: 1 0 7500 7500 0 -10000 10000
S: 1 1 -8000 -8000 0 -10000 10000