Version: 1.12.2-2.0.2.0_pre3.2
Issue: Attack helicopters duplicate infinitely over time, no idea of how that happened, causes massive lag on our server
Edit: They will keep spawning even though they are killed using /kill @e[type=techguns:attackhelicopter]
Screenshots: https://imgur.com/a/ToLW1c6

Strange issue. I suspect a mod compatibility issue since I never have seen before. The helicopter is linked to a spawn point (like the soldiers) which dissappear when enough mobs are killed. As long as there is a linked NPC there also should not spawn a new helicopter.