Let me start by presenting to you a scenario.
I make a house in Blender. The house has a door that animates open and close. I have a hard time getting the animation to work. I decide to make the house and door 2 separately imported models. This works fine. However, to get to this point:
In Blender, I opened the original house, selected the door, Delete door, Save as… House Only.blend.
Then, I open the original house file again. Select the House, delete the house, save as… Door Only.blend. Meanwhile, in Unity:
House works just dandy, but, the door has no materials of its own and I cannot choose a renderer or anything in the inspector.
Seems like anytime I try to make one blender object by modifying an original, Unity HATES it. I’ve had this happen with weapons and such, they jump to origin upon runtime, etc.
Can anyone explain this phenomenon to me? I post here instead of Blender forums because I like this community better 
There must be something I’m getting rid of that Unity needs. I’ve compared blender files and there’s nothing I can find.
Sorry about the length. Thanks in advance!