Its different with the arena. Its not the creature itself, but the history and whats linked to it in the map. Or the items that the caravans are carrying. Why, do you have any problems in one of your mods?
Its guesswork in this case... one crash was fixed by replacing a string dump in the xe (which i previously broke), another had to do with hives having a hive product but no creature inside, and a third one was using a minecart on a track, which started, but never reached its goal (because it was used in a reagent, and a dwarf stole it from the tracks => that will work every time, even in vanilla, so never use minecarts as reagents.)
