There IS a limit to the number of meshes in a Creature model... I ran into a similar problem with the Kalin Rider I did back in the Dark Sun CCC. Eventually, having tried hitting everything else with big bricks, I simply merged some of the meshes that shared textures and didn't have to move independently... Model immediately worked fine - with exactly the same polycount; I didn't REMOVE anything, just merged where possible...
But... NO, I can't now recall what I concluded the Mesh Number Limit actually was. But I do recall exhausting every other possibility for the rubbish crashing activity, so there IS a limit.
No idea whether such a limit exists in Placeables and Tile models, but if it does, it must be A LOT higher since I've never run into it...