Driver git version 5778f994d4. Exception is not handled in timer callback, so as with any thread pool threads exceptions the application domain goes down when server stops responding and first timeout is encountered.

Exception: System.TimeoutException: Timeout waiting for a MongoConnection.
at MongoDB.Driver.Internal.MongoConnectionPool.AcquireConnection(MongoDatabase database) in Driver\Internal\MongoConnectionPool.cs:line 141
at MongoDB.Driver.MongoServerInstance.VerifyState() in Driver\Core\MongoServerInstance.cs:line 233
at MongoDB.Driver.Internal.MongoConnectionPool.TimerCallback(Object state) in Driver\Internal\MongoConnectionPool.cs:line 268
at System.Threading.ExecutionContext.runTryCode(Object userData)
at System.Runtime.CompilerServices.RuntimeHelpers.ExecuteCodeWithGuaranteedCleanup(TryCode code, CleanupCode backoutCode, Object userData)
at System.Threading.ExecutionContext.Run(ExecutionContext executionContext, ContextCallback callback, Object state, Boolean ignoreSyncCtx)
at System.Threading._TimerCallback.PerformTimerCallback(Object state)