This is probably not Node Specific a general problem with connecting via a seed list.

ServerSelection via seed list is a great concept. It works poorly. I have attached an hour of starting a working webserver app and 30 times starting it in a little over an hour. It failed to connect over 40 % of the time. A larger amount of successful connections were made over 35 seconds which means they would fail in a hosting environment like Heroku. Only 10% of the time did it connect in < 6 seconds. Your support team is avoiding using seed lists in their troubleshooting. A tool would allow them to get the data of the API calls in question Lastly, this would cleanup a lot of bad answers to connectivity issues and then the port driver team could fix the problem.