Here's what happened: I set up a world border to be 100 blocks big, but the world border spawned in the middle of the ocean and there was only a chunk of the border in the world. (meaning, the rest of the border was missing.)
The next thing I know, it says this in chat: Shard suffocated in a wall.

I looked, but there was nothing there. It was as if there was an entity there or something. I tried moving around, but I was stuck. I seemed to be standing on nothing, but I was also stuck in the middle of it. Help please?