Block inventory slot 2 doesn't work

I'm using 2024.4 for forge, I have a GUI for a block that has inventory slots but slot 2 doesn't work. I can't put anything in it, manually or with a procedure, nothing happens. I can do it with any slot with any other ID but not slot ID 2 specifically. The only thing I can think of is that I originally had a slot 2 with itemstack pickup disabled, then re-enabled itemstack pickup but, I don't see why that would affect itemstack placement. I'm not sure what's going on or how to fix it.