Failed to load resource: net::ERR_INCOMPLETE_CHUNKED_ENCODING
You might want to check if the folder /var/lib/nginx is owned by www-data too. I had this problem that, when the response page was too big, the Nginx worker process tried to use this folder and failed, because it was owned by nginx and the worker process ran under www-data. By doing chown -R www-data:www-data /var/lib/nginx, the problem was fixed.
If anyone finds this in the future, my net::ERR_INCOMPLETE_CHUNKED_ENCODING were as a result of having run out of space. Have a look at your disk usage and see if that's why!
I've seen a similar problem on my Nginx Server running on the latest Debian. I'm running a Wordpress site with Advanced Custom Fields installed. On the advanced custom fields it says that the problem could potentially be with the max_input_vars value in the php.ini file. I increased my value from 1000 to 3000 and that fixed the issue on one of my sites.
You can check out this link to see if it might help you. http://www.advancedcustomfields.com/faq/limit-number-fields/