AFNetworking and strange error -999

Question

I have strange problem with AFNetworking framework. This problem is not common, it happens sometimes and I can not find the reason. It works 5 times in row and the next time, on the same request it returns NSUrlErrorDomain -999.

    [self patchPath:path parameters:nil success:^(AFHTTPRequestOperation *operation, id responseObject) {
           NSLog(@"OK");

    } failure:^(AFHTTPRequestOperation *operation, NSError *error) {
           NSLog(@"ERROR");

    }];