MongoDB field with Double data type saved as Int64 for no reason

Question

I have a case class with a field that is Double:

case class MyModel(amount: Option[Double])

I work with mongodb4 and use reactivemongo 0.19.0 with play framework 2.7.2 with Scala 2.12.8

from some reason, randomly, when I insert MyModel elements to the db amount field saved as int64 instead of Double, which is very weird cause most of the time not, just randomly.

its not a decimal point thing cause I saw other documents that this field don't have decimal point and it still saved as Double correctly.

what are your thoughts?

this is the insertion function:

  def insertOneWithoutEvent(doc: Doc): Future[Doc] = {
    doc.createdAt = Some(InstantNow)
    doc.updatedAt = doc.createdAt
    (for {
      insertedDoc <- collection.insert.one(doc)
        .map({
          case DefaultWriteResult(true, 1, _, _, _, _) => doc
          case dwr => throw new RuntimeException(s"$LogName was not inserted, something went wrong: $dwr")
        })
    } yield insertedDoc)
      .recover({
        case WriteResult.Code(DuplicateCode) => throw DuplicateKeyException(doc.uniqueIndexToString)
      })
  }