I've never had a map crash on Dawn City before, so no need to get overworked, Hobbes
After indepth analysis and many experiments, I think I know what causes the problem.
1. Spartan Scout #1 ends turn
2. Spartan Scout #2 tries to throw grenade
3. Game crashes - probably to LOF issues, since the throw is very tricky, going up the elevator.
All the equipment works normally, and after removing grenades from this spartan (and yet another one who tries to throw grenade inside a building as well), the game doesn't crash. The grenades work normally when the player uses them, as well as when AI uses them - most of the time, at least
They're vanilla grenades.
So my verdict is, OXCom engine + complex map = AI grenade throw crash (probably any arcing weapon will cause it, not only a grenade), probably due to AI trying to throw grenade up/down an elevator (the ladder, in this case). Otherwise, there is something peculiar about your ladders, Hobbes - make sure to re-check them
I can't pester the devs about this because it's not vanilla, so they'll probably tell me to beat it - mods are a hell to debug