RSS stopped updating (rss.xml)

I noticed having this problem a while ago and now finally found time to start dealing with it.

Pretty much at certain point of time rss.xml stopped updating and I don't see any of the new blog posts in rss.xml.

Any idea where to start looking? It was happening before I updated to latest drupal version, and after I updated it still didn't fix the issue.

Thanks for your help,
Vlad