Oven uses fuel but doesn't smelt iron

So I once sorted all my chests and I put every item that can be used as fuel for ovens in a shoulder and I wanted to smelt some iron. in the shulkerbox there were a lot of things including over a stack of trapdoors. I attached a Hopper to an oven and put the shulkerbox on top. while it smelted I knew I'll need more iron so I went mining and got more iron but the shulkerbox was completely empty when I was back and I got only 31 iron bars. I mined way out of render distance so that probably has something to do with this, there were also items that I thought could be used as fuel (string and feathers) but weren't fuel. Please fix this.