Hello!
UserUtteranceReverted reverts everything after the user’s message - including setting the slot.
I don’t know if events (the list in return) are processed in order and if that order matters. If yes, try to to revert the utterance BEFORE setting the slot:
return [UserUtteranceReverted(), SlotSet('safety_net_count', safety_net_count)]
If this does not work, try to use ActionReverted() instead:
return [ActionReverted(), SlotSet('safety_net_count', safety_net_count)]
If this doesn’t work as well, please explain more about what you’re trying to do so I can know if there are other ways 
I suggest you also read this thread: Difference ActionReverted and UserUtteranceReverted.