I use the FD feedburner plugin to redirect all feeds of my self hosted WP site to Feedburner. That has worked fine until December 2013. Since then the redirection doesn't work anymore. The feed validates fine. The same is true if I subscribe the feed through the Thunderbird RSS reader: posts after 12/2013 are not showing. If I export the posts to a blank WordPress installation, Thunderbird shows all posts in the RSS feed.
I'm totally stuck here. Why would WordPress include posts until December 2013 but not the recent ones? And why does it work when the posts are imported to a new blank installation?
Would be glad for any help. Thank you!