The Improved Blast Furnace of Immersice Engineering does not accept Iron through a hopper on the top.

I tested the same thing in an Immersive Engineering only instance and it worked. Both coal coke and iron blocks or ingots were accepted through the top.

In Cave Factory the Improved Blast Furnace only accepts coal coke inserted through a hopper. Neither iron blocks nor iron ingots can be inserted that way. I observed this in Cave Factory 1.0.2 and Cave Factory 1.1.0.

Unfortunately this didn't work for me. Do you have pre-heating installed?

A way around it is to use a dropping conveyor from Immersive Engineering. It'll only work with iron ingots though, but you can still automate it. Coal Coke and Coal Coke blocks work both for hopper and dropping conveyor for me.
If you're using a magnet, use the covered conveyor to stop yourself from picking the items up.

You can fix this by removing all lines in your kubejs/server_scripts/recipes.js file that contain immersiveengineering:blast_furnace or immersiveengineering:blast_furnace and immersiveengineering:steel
This will set back the recipe for steel to default though, so 1 iron/steel.