Tashgar mission bug

So during the mission 'Tashgar', after the ride to the damn, I begin to engage the enemies at the entrance of the damn. After destroying the helicopter though, the mission doesn't advance since, I assume, you need to kill all the enemies in the area. After a while, I noticed that one of the enemies is constantly falling through the map every time I restart the mission (I played the damn mission 5 times already). This is really annoying that problematic to me because it's just ridiculous to find in a game like this.