It's because you didn't recalculate the NavMesh. The 1.3 update screws up everything. You have to put it all back. I know this because I can see beyond the things that are right in front of me. You say this ends up with thousands of duplicate entries. This is WRONG. The engine puts things there for a reason. You have to think about why it puts what where. Run the calculations. If you could use the same programs as I pretend to, you would see this as clearly as you see anything. :shocking: :bonk:
I see... so it was you all along!

Anyway, at first I thought this would be faction related, or maybe because some NPCs in there were non-persistent and in a different cell.
So in case getOwner returned a faction, I did a refwalk on nearby actors belonging to the faction, and used SendAssaultAlarm with the single actor as parameter. But that's crashing as well. Can't really believe that function produces CTDs in general, since it's used in a good number of vanilla scripts...
But I'm using SendTrespassAlarm now, which does the job as well, and more imporantly doesn't crash.