Hi @abhinoy,
Welcome to the community! 
You have quite the interesting issue there. Can you do the following check for me?
- Run each request in the collection individually, see if you can isolate one request thats having the issue.
Can you provide a bigger screenshot of the issue? This might be difficult to troubleshoot but we’ll try. Its possible that your endpoint is reseting the connection for some reason, maybe due to quick succession of requests. We might have to add a delay but for now, lets isolate the issue to see if its exactly only when the collection is run as a whole, or if there are specific requests that trigger it.
Best,
Orest