Some chunks of the world glow like light source blocks, and digging or placing blocks within those glowing chunks does not change their appearance. There is no hitbox on the actual broken part. The avatar can be stuck in the broken part. The avatar will then be in a spectator-like viewpoint. The blocks you place there will become transparent. Furthermore, blocks moved by opening and closing doors, pistons, etc. are not visible, which causes problems even outside of survival. This bug occurs only in multiplayer. Even if there is no lag.