It's not a bug, it's because the settlement is abandoned and in use for scav clearance missions.
If the target of your 'massacre' only has one base in the entire galaxy, this will happen quite often.
The solution is to check where the faction has a presence before you accept the mission. Go to their home system in the galmap, open the system map, look at POI and check the list of odyssey settlements. If they only have one, don't take the mission.
If the target of your 'massacre' only has one base in the entire galaxy, this will happen quite often.
The solution is to check where the faction has a presence before you accept the mission. Go to their home system in the galmap, open the system map, look at POI and check the list of odyssey settlements. If they only have one, don't take the mission.