I am trying to bulk insert documents into MongoDB (so bypassing Mongoose and using the native driver instead as Mongoose doesn\'t support bulk insert of an array of document
This also happens if there's a duplication of of the _id value. Most situations will be when you might create an new record from an existing record.
_id
Deleting the _id and inserting the record and letting Mongoose/MongoDb take care of the creation of the id.