Single PWM Channel Fails to Update, Pixhawk 4 (7/8 main PWM are ok)

Using a custom module, publishing to group 0 with a custom mixer set up as a pass through. Hardware is a Pixhawk 4 (and I checked two separate Pixhawk 4s to make sure it wasn’t a HW issue).

This code worked when I used it in an example:

However, when I set it up to run in my custom module, channel 4 (control[3]) fails to update at all, while the other channels all update correctly:

Manually testing the channel is succesful (using pwm test -c 4 -p 1100, for example).

I’m very confused as nothing should have changed between the example code and the new module code. What could be causing this?

Appreciate any help you all can provide!

I checked dmesg in the mavlink shell and got a low stack memory warning:

Not sure how to check for the culprit, I assume this is related.