This happens on Minecraft 1.21 with Fabric Loader 0.16.0

Sometimes it will let me load a schematic, but the moment it is rendered on screen, the game crashes.

This happens with both the current releases for 1.21.

Attached are the latest.log and the error log associated with the issue.

latest.log
hs_err_pid27608.log

Seems like it may be an issue with Iris, as disabling my shaders prevents the crash. Unsure though, since I cannot read these logs well.

Edit: I have also confirmed that reenabling the shaders while a schematic is loaded crashes the game.

Shaders are a known issue with litematica as it messes with the rendering system and litematica doesn't know what to do. Currently there is no way to have shaders and litematica so you'll have to pick which one you want

Interesting, It had faired just fine in older minecraft versions. I have played on both 1.20.1 and 1.20.6 with both shaders and litematica, and had no troubles.

Does this happen with all shaders packs, or also without shaders active (if you still have Iris installed)?

I only use Complimentary Reimagined.
Iris can be installed, as long as the shader is disabled, the crash does not occur.