Check for firmness of the safety slide and spring itself.

The other variable is the top lever spring. A weak spring COULD cause the situation where the top lever is getting bumped open under recoil some thus resetting the safety. But i find this unlikely on a fox given their use of a pretty stiff coil spring for the top lever.

Is the safety fully going back or jjst enough to cause blockage of the triggers?

B.Dudley