GZIP compression not working

Seems like GZIP compression suddenly stopped working recently.
– I’m using minify JS and CSS
– I’m also using Cloudfront CDN

My pages only load the normal css and js files (tried with minify both on and off, and CDN both on and off). No matter what, gzip files are not being used.

http://ww.wp.xz.cn/extend/plugins/w3-total-cache/