This is a graphical glitch that occurs when a player views a barrier block that they are standing on top of. Barriers will render their texture very large if the player is standing on the exact middle of the barrier block. The barrier texture can be rendered many times larger than the block it exists at if the camera is looking down on it. See the screenshots.

Steps to reproduce:

1)   Go into a superflat testing world, preferably one with stuff in it.

2)   Run these commands yourself:

3)   /gamemode survival

4)   /kill

5)   Respawn, but don't move the player.

6)   /gamemode creative

7)   /give @p barrier

8)   Hold the barrier in your main hand.

9)   /setblock ~ ~-1 ~ barrier

10)   /tp ~ ~ ~ ~ 80

7)   Have a look around...

If this is TLDR that's okay. Read it only if you need it:

Note that none of the commands used here have anything to do with the glitch, this was just used to center your player on the block.

Now don't move anywhere, just look down and you'll see a blotch of red. It might even cover the whole screen (or just one block).

Jump up and place another barrier block below you, so they are stacked on top of each other. Now the red should fill your screen.

Try flying straight up (never move away from where you are, though), you'll see the barrier's texture enlarge and cover a substantial amount of space. Look straight down and start slowly looking up, and watch as the barrier block's texture grows, getting very large very quickly. If you keep looking up, the texture will probably disappear before it leaves the screen.

If you're not getting any of this, retry everything in an empty superflat world, exactly as it's written. But if you can see the rendering glitch, try experimenting with it some more. Also, some thing to note: try panning the camera while looking at the giant barrier texture, and if you keep panning slowly, you can see that the texture will snap to the X or Z axis when it gets close to it. Maybe that's intentional?

This was a fun little bug to play with, I hope it'll be easy to fix. Also I really appreciate the work you do in fixing my game, thanks very much for your effort. Good luck