I was moving around in the desert but then I noticed that the screen started to glitch and make flying stuff like black pyramids etc. I thought that it was from my PC but then I realized that it was from the game itself when I took the picture of the situation.
I was looking exactly at the south east when that happened, when I turned around the glitch wasn't appearing but it was only appearing when I look at the south east.
The server is modded. Can you reproduce this in a vanilla environment (client and server)?