Sometimes when I join a friend's realm, if I'm in a cave it might sometimes bug out and there'll be full sky light there for no reason. This usually wouldn't be much of a problen, but it becomes an issue when it's around a mob spawner grinder. I want to get XP, but the mobs die of sky light before I even get to kill them. Even when I go far away and then go back for the chunks reload, it doesn't get fixed. Pressing F3 + A to reload the chunks doesn't work either. I tried updating the lighting by placing torches around, but that didn't work either. Relogging doesn't work either. I have no idea how this happens. I haven't yet tested if other players have the same problem at the same place yet, but I'd assume so, since the mobs are getting affected by the bug, meaning it most likely has to be server-side.