Getting MongoEncodingError with a Date field

We are trying to Sync a MongoDB Cluster with Realm but we keep getting the following error:

Error:

Failed to convert MongoDB document to configured schema during initial sync

Source:

Error syncing MongoDB write

Logs:

[
  "Namespace: loop_server.projects",
  "Document ID: ObjectID(\"58a321a2cfb7c47c15043b18\")",
  "Detailed Error: error encoding document during initial sync: could not convert MongoDB value to Realm payload for { table: project, path: createdAt }, value=[{date 2017-02-14T15:26:26.137Z}] : unsupported BSON type for Realm value primitive.D"
]

I have already made sure that all items in the collection have a “createdAt” value that is a date. And in my Schema I defined it like this:

"createdAt": {
  "bsonType": "date"
},

I really don’t have a clue what can be causing this error.