I have another mod which greatly increases maximum stack sizes. However, with Iron Furnaces this line causes a massive list to be created which quickly crashes the game. What is the reasoning behind this implementation?

That line of code is wrong, will push an update soon.

I'm having the same problem on 1.20.1, everytime i place down a netherite furnace or place a augment on it, the game freezes for a few seconds, and when i placed a stack of 1000 sand, the game froze entirely and bricked my save so hard i had to uninstall the mod to get back in