I thinks it's probably a chunking loading thing, the black area is the area that your client haven't load in yet, it'd disappear when u look at it loads it in. You can press f3+g and check if the edge of the black area lines up with the chunks.

@JustJams I am always in my base too, so it is always loaded @CreeperLord170

@CraftyMyner

Sorry, I actually meant the chunk being displayed on your client
Although I not very sure if I'm right though

@JustJams I would like to point out there is no bug reporting section and this seemed like the smartest section to post it in.

If you want to report bugs with the game try the Minecraft Bug Tracker!

Also a helpful place to check if someone else has found the same bug and reported it. In this case it looks like someone beat you to the punch by about 3 years :P
https://bugs.mojang.com/browse/MC-63020

Bugs like that are mostly a Mojang issue, not CM. Only reason I can see to have a Bug Report section is if something isn't working with spawn, like the hats, or arena.

@CraftyMyner it's the same thing with the invisible glitch

@CraftyMyner
Apparently that's fixed in 1.12! Keep your fingers crossed that it's gone for good :)