That means you catched a very rare bug that makes battle system hang itself on it's code.
It can happen during saving on the location with an enemy and then immidiatly loading save file back. It's very annoying to deal with and we are looking for a fix since adding system in.
Possible solution is loading a save file before coming to goblin's location and proceeding forward. It should fix it, as the fire sword must shot them with one hit, no matter what. As it has a priority over anything else.
And if it doesn't work then we have a big problem...