I’ve reproduced the problem, and it is caused by the parameter TRIM_RC_AT_START. That defaults to off, but was enabled in your parameters.
There is a bug in the handling of this parameter.
If you set TRIM_RC_AT_START to 0 then it will fix the issue for you.
TRIM_RC_AT_START is not yet documented and I don’t have info over it, but I can confirm that it solved that issue.
I have rebooted the board and didn’t lose the servoxx_trim values. GREAT!
In this model I reported another thread “Servo jitters in stabilize and FBWA” that isn’t has important but is a odd behavior.