Autoturrets not killing npc

Hey question.. I have bases setup with turrets on the front and when the npc's parachute in the turrets dont kill the npc's The turrets do shoot at them but they dont go down.. is this a glitch or a setting needs changed?

Npc are immune to damage untell they land

yes they've landed and are running around in front of the turret. Its firing but not killing the npc

are you using truePVE or anything?

TruePVE.. Yes we use that