Swagger Nginx flask-restplus
Similar question: Server response gets cut off half way through
Nginx needs to have permissions to write to a temp folder when sending large upstream files. Usually you'll see it in the /var/log/nginx/error.log like
2018/06/28 16:34:48 [crit] ... open() "<tmp folder>/x/y/00000000z" failed (13:Permission denied) while reading upstream, <request info...>to fix this you chown to nginx:nginx (unless you've changed the user manually) eg sudo chown -R nginx:nginx /var/lib/nginx. if the permissions aren't at least 7xx you may have to change that but that shouldn't be an issue.
alternatively you can set proxy_buffering off; but that isn't recommended if you expect the connections to be longer than usual (speed or size).