On multiplayer servers like Hypixel, CubeCraft, or Performium, lighting on stairs and slabs is off. The open part of the stair or slab has no lighting at all.
Small scale servers, like realms, LAN games, or singleplayer servers do not have this problem. Mineplex US (us.mineplex.com) and Mineplex EU (eu.mineplex.com) do not experience this problem. Try the servers I mentioned before you try any other servers, as these servers definitely have the problem on my computer.
This is most likely because the block is counted as filled in and as such cannot contain light, but it's a slab, so it should contain light.
How to reproduce:
Run Minecraft Client
Join Hypixel (mc.hypixel.net), CubeCraft (play.cubecraft.net), or Performium (mc.performium.net). If you are a Mojang employee, some people would be happy to see you.
Explore the lobby, and if you notice a lighting issue on slabs and stair blocks, you found the glitch.
This may be a problem with the individual servers themselves. Their plugins may be causing this problem, and that may explain why small scale servers without plugins don't have this problem. You can try asking the server administrators what plugins they use and investigate.
Thank you for taking the time to read this.
Thank you for your report!
However, this issue is Invalid.
Your game, launcher or server is modified.
If you can reproduce the issue in a vanilla environment, please recreate the issue.
Any non-standard client/server/launcher build needs to be taken up with the appropriate team, not Mojang.
Any plugin issues need to be addressed to the creator of the plugin or resource pack.
If you have problems on large servers, such as The Hive and Hypixel, please contact them first as they run modified server software.
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