Graphical glitch which seems to be lighting related. Refreshing the app, exiting the world, and messing around with the settings didn't fix it. The black tiles disappear on contact with light ( torch, projectiles, etc.), although they reappear immediately after said light is gone. (Edit: light sources do remove them.) Placed light sources won't get rid of them if there are blocks between it and the black tiles. This is on ios.
Note how the black tiles on the left are missing. After the Zenith projectiles returned, the black tiles were back.
Last edited: