Check models.dat.. make sure it's using ky.snd and the number of models is correct.
Some of the 3do's for unknown reasons crash the game on occasions (I think the Mousebot is one of them that has problems, and stack of mines, etc).
The ones that are stable I know are (at least some of the total list of stable models for MP):
rail detonator (or any hand gun but the bryar and "blaster")
rancor (if it's MOTS)
The best ones have you being about normal size and not floating (much), and are "one piece" (ie: not a full animated model like the rancor or ATST).