{
  "type": "minecraft:block",
  "pools": [
    {
      "rolls": 1,
      "entries": [
        {
          "type": "minecraft:item",
          "functions": [
            {
              "function": "minecraft:copy_nbt",
              "source": "block_entity",
              "ops": [
                {
                  "source": "lava_level",
                  "target": "lava_level",
                  "op": "replace"
                }
              ]
            }
          ],
          "name": "starwars:iron_forge"
        }
      ]
    }
  ]
}

the block has an int nbt tag called lava_level, this is the blocks class

https://github.com/EILFYT/StarWarsMinecraftMod-1.16.5/blob/main/src/main/java/com/eilfyt/starwarsinminecraft/blocks/IronForge.java

post debug log