Mobs do not render or render very strangely

When I attempt to spawn mobs and armor stands (they are basically mobs), they either don't render at all or render very strangely, rendering only the legs, and an additional leg in the center of where their body would be.

I'm sorry I don't have any screenshots, as the mobs just changed to being invisible. All the mobs are either invisible or rendered in that strange fashion, there cannot be some of both.

In addition, when the mobs were rendered strangely, it seems that when they moved farther away from me the textures became more flat and enlarged, but still used only the leg textures.

I can still punch the mob, and upon killing it, it will drop items, but it simply doesn't render.

I have never had any problems with rendering in Minecraft before. Is this a driver problem?