Well the AI will fight each other. That would be the most likely reason. You said they were "selfdestroyed" but that is most likely not true.

Yea but there were NO intact Enemys just destroyed and Grounded ones i Checked the complet List of all Grids only Groundstations are Intact, looks like they cant Fly and crash themself

i think i got the problem... i think they run out of fuel / energy and fall down?

is there a way to get around this problem?

I got a similiar issue actually. Orbiting Europa, and there seems to be some spot of interest to a faction called THIES on the moon. They got drones spawning there, piling up at the same location. Eventually, they run out of fuel and crash onto the same spot, making a crater bigger and bigger and bigger...
First I thought they want to get to a grid there and act as support, but after cleaning everything via admin menu, they keep on coming. Eventually I will have to fix the voxel damage somehow, but I would love to figure out how to prevent that faction from spawn spamming, or at least have the grids despawning after some time.
The same faction spams space stations around me as well. Basically their spawn rate is nuts. But maybe thats because I don't have any of the other MES running so the mod force spawns always that one same faction instead of several ones?