NSURLSession keeps giving errors like 1001, 1003, 1005 etc

Question

I have recently moved from NSURLConnection to NSURLSession i.e., I have replaced all implementations of NSURLConnection with NSURLSession. I have done this so that my code is up to date.
Everything works fine except that I now keep getting a lot of errors which were never there with NSURLConnection. For eg., I keep getting 1001, 1003, 1005 etc intermittently. I am pretty sure that the connection is good and strong. I do not go out of network too.

My implementation for NSURLSession is as follows:

NSURLSessionConfiguration *sessionConfiguration = [NSURLSessionConfiguration defaultSessionConfiguration];
    sessionConfiguration.timeoutIntervalForRequest = 60;
    sessionConfiguration.timeoutIntervalForResource = 60;
    sessionConfiguration.HTTPMaximumConnectionsPerHost = 10;
    sessionConfiguration.HTTPAdditionalHeaders = @{@"Connection": @"Upgrade"};

    _mySession = [NSURLSession sessionWithConfiguration:sessionConfiguration delegate:self delegateQueue:nil];
    _responseData = [NSMutableData data];

And here is how I create the task:

    NSURLSessionDataTask *myTask = [self.mySession dataTaskWithRequest:inURLRequest];
[myTask resume];

I would appreciate if anyone can help in this regards. :(

Thanks in advance.