Servo_9 thru Servo_16 Trims Not saving

First post here,
I’m working on a project with an electric 8-motor airplane. I’ve tuned it already and have flown auto flights with it numerous times (to give some context of where it is functionally).
I am trying to add reversing thrust but I am running into some issues. Since the aircraft is multi-motor, I have mapped servo outputs 9 thru 16 to the throttle signal. This has worked out fine thus far, but when I started to try and add reverse functionality I noticed that when I updated the trim value for these servo outputs, it didnt save for some reason. In mission planner I update the values, write them, and it returns that they have been saved; however, upon next boot up, when i read the trims, they all revert back to 1000us. This seems to be blocking me since from what I can see, the trim value is what the flight controller reads as a zero rpm input. For reference these are my ESC settings
Max Reverse: 1000
Neutral: 1388
Max Forward: 1950
The reason the forward has a great PWM range is because I would like to have more fidelity there.
Any input would be greatly appreciated.