We are running a long haul test against a single mongodb host using the C# driver. We have a database with 300K collections. We run 500 queries per second and 0.1 updates per second (x10 of our production workload). We found that after about an hour, all reads hang. We don't have the stack trace.
Looking at the code it seems that ByteBufferFactory can potentially hang in case of network issues etc.