Reading the log I could found this:
In use pin no longer exists on node Calculate Health . Please refresh node or break links to remove pin. from Source: /Game/Blueprintts/EnemyCharacter.EnemyCharacter
It seems the function is there, but at some point you might have changed its parameters and it wasn’t properly replaced on your EnemyCharacter’s Blueprint. I suggest you to take a look on it and check if it will compile files (maybe you just remake that node with the exact same way…just to make sure)