I'm honestly not sure? Unity has so many different things that do the same thing so it's kinda hard to keep track of. But let me know if you get any updates, or they need more info from me. I also made this forum post about the issue, but it kinda accidentally turned into a journal: https://forum.unity3d.com/threads/canvasrenderer-crashes-unity-when-given-a-mesh-that-has-submeshes-more-than-one-material.439133/