I suggest you read this post and then this post.
The beats input adds a [host] object to the event, the file input adds a [host] string to the event. A field cannot be an object on some documents and string on others. If you decide you want [host] to be an object you can do a mutate that is conditional upon [host] being a string. If you decide you want [host] to be a string then make the mutate conditional upon it being an object. Then once you start over with an empty index you should be OK.