404s on AWS deployed MEAN app

I have a MEAN.io application deployed to AWS EC2. Its running via Nginx proxy pass on a 8087 port, config is as follows:

location /myapp/ {
        proxy_set_header X-Real-IP $remote_addr;
        proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
        proxy_set_header Host $http_host;
        proxy_set_header X-NginX-Proxy true;
        proxy_pass http://0.0.0.0:8087/;
    }

The problem I have is that in the browser some POST/PUT requests sent via AJAX are returning 404 errors and default nginx error page. Those requests are not even making it through to Node.js server as I can see in the logs that they are not recorder. There is definately a route provided for those requests, as the app works totally fine on localhost. The same POST/PUT requests seem to work fine when queried directly using 'curl' in the console.

I am not an nginx / AWS expert, so I wanted to ask simple question - is there anyway nginx could be caching those requests and why would they return different HTTP code when queried from 'curl' or via AJAX in the browser?