I have noticed this same issue before on my own servers, I am believing that it is a known bug that has never been fixed with the game's renderer, but I am not certain of this. For me, it has happened intermittently so it is possible you are dealing with something else here.
This model was most likely a port from some software called miku miku dance (A 3D animation tool).
If that is the case then it is safe to say it was not optimized to be ran on Gmod or any other game on the source engine.