Django Err_empty_response or connection reset

I have a django app and it is accessed via digital ocean auto generated ip address. I used to have this issue but it was not that often but today it was happening in every click. basically issue is when navigate to another link it gives me two types of errors. sometimes err_empty_response and sometime connection reset. most of the time the page gets auto reloaded and works fine. but real problem is when i have to submit the form. Basically i followed this tutorial to setup my server so you can assume that i have exactly same settings https://www.digitalocean.com/community/tutorials/how-to-set-up-django-with-postgres-nginx-and-gunicorn-on-ubuntu-16-04