I've beat Grym about 5 times now on Balanced, Tactician and Honour modes. At least 2-3 of those times, Grym was directly overlapping the crucible. Only once I could not insert Mythril to get a second piece of equipment.
There was
previous thread regarding this:
I realized there were two mithril veins and I had missed one. I cannot interact with the crucible and the mold-thing is stuck. I think this is not a bug so much as it is a flag. Let me elaborate. It locks the forge when there is no more mithril in your inventory. if you have two, use one, you can use it again on the second, but if you only had one to start with, the game doesn't recognize that you could go get the other and come back.
My suggestion is, if you have more than one save file, go to a save BEFORE you inserted Mythril into the Forge. Make sure you have two pieces of Mythril in your inventory, then beat Grym. See if you can get two pieces of equipment that way.