In 2.x, all fields must adhere to the same data type or you will get a failure [1]. To quote:

  Fields with the same name, in the same index, in different types,
  must have the same mapping

So hopefully this isn't an issue anymore! I do strongly suggest (and we've done this from the beginning) that no one rely on elasticsearch's auto mapping and that you should explicitly map your fields.

[1] -- https://www.elastic.co/guide/en/elasticsearch/reference/curr...