Nginx+PHP-FPM intermittent blank page

Hello, I been suffering with this problem for a few days on a new server, some times like 1 or 2 times a day the Home page of wordpress shows a blank page with a 500 error (only visible from Chrome console) and it stays like that for a couple of minutes where not even a hard refresh (ctrl+shift+R) seems to work, but eventually it comes back to normal. the only way to quickly fix it is to stop nginx, delete nginx cache at /var/cache/nginx/ and start nginx again.

The server is a CentOS 6.5, nginx/1.6.2, php 5.3.3 (php-fpm). my site conf: http://pastebin.com/W9x4r57w http://pastebin.com/ryJ7NxT2 (maybe is a little tweaked from fail fix attempts but still functional 99% of the time)

The same error happens on a few selected pages but not in the post pages inside wordpress, so even when the homepage is blank the rest of the site works ok.

I use the same conf on other servers and websites but this is the only one causing me trouble, the main difference is this website has a lot more traffic (2k+ per hour).

I been looking around for days but nothing seems to solve it, now about the pages where the error occur this pages read a TXT file with a “cached version of the page” which is refreshed/rewritten every 2 minutes, this help us to load super fast the homepage (and some internal pages) which usually take a few seconds more to load without the “cache” text file.

Note: We use CloudFlare but the error shows even if I use my hosts file to connect directly to the server (no caching in the middle) my PC <–> Nginx

Any ideas or suggestions would be really helpful. Thanks.