I play with Optifine and I've been playing on my single player world recently, and came across Pillagers that were invisible. At first I thought it was maybe particles being turned off if they had invisible potions, but it wasn't after checking. After that I left and re-entered the world, and the Pillagers were fine after that, but then I saw the Skeletons were also affected by this? It looked like the models just weren't registering. I'm not sure on how I should get a video on it, because I can't run any recording software currently.