I checked with the WPEngine team and they mentioned

Hi guys, I checked with the WPEngine team and they mentioned the error with my RSS feed is caused by your plugin Slide-In. Any ideas?

http://feeds.feedburner.com/openbriefasia

This page contains the following errors:

error on line 532 at column 80: EntityRef: expecting ';'
Below is a rendering of the page up to the first error.