something may have clipped into the anvil and its hitbox is impeding workflow....

Can you swing your hammer at Items/ingots when they're not close to the anvil? If no, I would probably copy save files, back them up somewhere if you really care about them, and delete the save appdata/local/shopsim folder entirely, and see if you can hammer in a brand new save...

If you can swing at other things but not the anvil, Try taking one of your present crates over to the anvil and try working it onto the anvil from different directions - This might be able to help you learn if something is stuck in the anvil's location.

Alternatively, Get a pole grip and place it near the anvil in a way that you can rotate it through large areas of the anvil, and stir it around inside and see if it gets caught on anything, or if it forces something out/removed - and afterwards - whether you got a reaction or not, try hammering again.