For players, when a VisualSet is used, the game is going to look at the first model field for all Visuals (Visual 1, 2,.... thru 9). The problem you're having is all of the flesh golems have extra appearance options under each visual, that the game will automatically apply to a player character. "unassigned" is not an acceptable visual indicies for a player.
To remedy this, you need to copy one of the root models, in the root models section. You then need to copy the visualset of the model, which you will find in the resource manager.
Once you have copied the visualset over, you can now remove the model parts the game is calling for that you're not wanting. There should either be one or no model piece under a Visual (visual 1, 2... etc). Since this is an NPC, remember that the Visual # does not correspond necessarily to what piece of the character model it's affecting (that's defined automatically based on the model piece being called for). So for NPCs, you will frequently find there is no "leg model" (it is "unassigned") because the lowerbody/trousers model already includes feet/legs in the piece.
Hope that helps.
