Enemie AI, random spawning

I know it’s been a while since this game came out so most of you are aware of this already, but does anyone else get frustrated at the random spawning of enemy AI during some missions? This is most common during those side missions where you have to defend the radio tower.

Yesterday I did that mission where you have to find the underground Unidad base and get cartel data (can’t remember the region). Anyway, after clearing out all enemies all I had to do was defend my position for a minute and a half. This would’ve been a simple enough task would an entire squad of Unidad not have spawned literally right under the mezzanine where I was taking cover. Didn’t even give me a chance to find another spot, literally just spawned right under me.