When we create a ReplicaSetMonitor for a replica set for the first time we don't kick off a refresh of that replica set. The ReplicaSetMonitorManager will eventually refresh it, but it only refreshes all sets once every 10 seconds. This means there can be a period of 10 seconds or more (if it has to wait for other sets to be refreshed first) before all nodes of a replica set are discovered. This can cause us to neglect certain secondaries for secondary reads, preventing us from evenly distributing the read load of secondary reads until after the full refresh takes place.