When facing a direction between certain yaw values (varies with height, and wider range of invisibility with height), entities (shulkers, for example) become invisible. The videos show a shulker at y=1000 and one at y=300. The one at y=1000 is only visible within a short 'slice' of vision, while the second one is usually more visible.
I do not know if this is intended, but it seems strange that it should happen.
I tried another shulker at y=256 and it was visible from all angles, so it gets worse from there.