Even after all this time I am still trying to understand the way city revolts work.

With revolts from your faction to rebels it draws upon the rebel tribes, but when your conquered settlement reverts back to the faction you took it from it seems to depend upon recruitment buildings already present - remove all these before it revolts and you get an empty settlement after the revolt...

But, in my build at least, mercs active for hire in such a region cause a CTD when this revolt occurs (to former faction, not rebels). If the merc is not present then it revolts to an empty settlement (assuming no recruitment bldgs). If there are recruitment buildings the merc will be found in the settlement. Mercs are set to slave and to the faction ownership of the land in which they are hireable.

This is very perplexing.