under some load (~100 concurrent threads), the driver throws the following exception:

"MESSAGE: Unable to connect to a member of the replica set matching the read preference Primary
STACKTRACE: at MongoDB.Driver.Internal.MultipleInstanceMongoServerProxy.ThrowConnectionException(ReadPreference readPreference)
at MongoDB.Driver.Internal.MultipleInstanceMongoServerProxy.Connect(TimeSpan timeout, ReadPreference readPreference)
at MongoDB.Driver.Internal.MultipleInstanceMongoServerProxy.ChooseServerInstance(ReadPreference readPreference)
at MongoDB.Driver.MongoServer.AcquireConnection(MongoDatabase database, ReadPreference readPreference)
at MongoDB.Driver.MongoCursorEnumerator`1.AcquireConnection()
at MongoDB.Driver.MongoCursorEnumerator`1.GetFirst()
at MongoDB.Driver.MongoCursorEnumerator`1.MoveNext()
at System.Linq.Enumerable.FirstOrDefault[TSource](IEnumerable`1 source)
at MongoDB.Driver.MongoCollection.FindOneAs[TDocument](IMongoQuery query)
at MongoDB.Driver.MongoCollection`1.FindOne(IMongoQuery query)

if we remove the replica set from the connection, the problem goes away.

I saw another issue mentioning this problem where removing "disconnect" solves the issue. we don't use disconnect.

this is a blocking issue