Is people on your club slowing down the plane before flaps down?
Excess speed would be my guess as the cause. We don't know what the load on the servo is without some sort of logger or telemetry, so it's anyone's guess how slow is slow enough to use flaps.
Full-scale have flap and gear limit speeds for just this reason. If one lowers the flaps at excess speed or get too fast with them lowered, the flaps can 'blow up' (retract or fail unexpectedly).
on my uf and viper I wasn't really concerned about my speed when I deployed the flaps.
You may be abusing the flaps & servos if you're not slowing down first.