Render Thread/FATAL

I have created a few entity models and textures and was trying to build a version to see how they are in game. While trying to build the project it crashes with the error [Render thread/FATAL]. Any ideas what could be causing this and/or how to resolve it? I've done this before with other entities and haven't had this issue before. 

I'm using MC 2024.1 for forge 1.20.1