That’s a WebGL context loss or texture size error. Remove the pack, lower mipmap levels, or reduce render distance.
To get that premium aesthetic, you need specifically compiled PBR (Physically Based Rendering) shaders or clients that have them pre-baked. Here is the definitive look at the best ways to upgrade your Eaglercraft experience. 1. The "Pre-Baked" King: Astro Client If you want the easiest path to a beautiful game, Astro Client shaders for eaglercraft best
If you are playing on a school Chromebook or an older device, "Lite" shaders are your best bet. That’s a WebGL context loss or texture size error