Provide at least the following information

• Minecraft version - 1.21
• litematica version - litematica-fabric-1.21.1-0.19.50.jar
• malilib version - malilib-fabric-1.21.1-0.21.0.jar

When I placed the attached schematic into the world, the game crashes. I believe it has something to do with entities in the schematic since looking at blocks in the schematic do not crash the game.
Firework Farm.zip
crash-2024-08-29_19.27.28-client.txt

Since I'm playing with a kgjhillion client-side mods, it's possible that it's an incompatibility issue with some other mod.
I've tried with disabling sodium, iris, and entity model/texture features and the crash still occurs, so I do not know which mod that's causing it.

It's an issue in something called Polytone. It's trying to do something while entities in Litematica's schematic world are being rendered, and it tries to cast the schematic world to a vanilla ClientWorld, but the schematic world does not extend the ClientWorld, so it crashes.