The locking of landing gear is not a feature I coded in. I know how this can be done in the flight_model.cfg parameters.
"gear_locked_above_speed =0" is what I used so that it is not affected by speed.
This may be a conflict with some of your add on aircrafts??? Unfortunately I can not duplicate this, so not sure why you are having an issue. Have not heard this from other users either. See if this problem persists with solo flights, or not using any add on aircraft in the scene. Wish I could offer more suggestions. 😕