Some mods (or possibly even large enough Resource Packs) can cause a ConcurrentModificationException with this library. The way to fix it would be to change the mixin in TextureManager to target the lambda that calls register instead of calling the mixin code right before returning the CompletableFuture which could still be running code.

Here are the logs that were posted in a bug report involving Nostalgic Tweaks and this library causing the game to crash: https://paste.ee/p/ftqqd

I wont be home for the next 1.5 weeks, after that I can look into the issue