In last couple of releases, Mongo has been changing their API quite a lot. I’m not a Mongo expert, but it looks like the client is attempting to set up a connection to a cluster, but finds a server in standalone mode.
Instead of using the MongoFactory, you might as well directly create a MongoClient instance using their own API. There, instead of passing a list of a single node (ServerAddress), pass the ServerAddress directly. This prevents the behavior of attempting to connect to a replica set.
Allard