Why isn't my RSS item appearing in a filtered news feed?
Bear in mind that every implementation is different, and your news system may not be set up in the same manner as the following solution. This answer refers to an RSS-based news system that uses tags for filtering and sorting.
For RSS items to appear in a listing or feed that is filtered via the tags in page parameters, the RSS item itself must have the appropriate tag. Generally, when a new article is published and the RSS item created, the item inherits the tags on the article. However, subsequent edits to the article tags don't affect the RSS item tags, and vice versa.
If your news solution filters RSS items by tags, and an item is not appearing in a listing when it should, check the RSS item for its tags.
Why aren't I seeing any events in my events RSS feed?
If an RSS feed is being used for events, only items with a publish date set for the future (i.e., the scheduled date of the event) appear in the feed. Add a new RSS item or edit an existing one with a future publish date to see it in the feed.
I created/edited an item but I'm not seeing changes in the RSS feed.
Rebuild the feed to incorporate any new items or changes. Level 7 users and higher can rebuild RSS feeds from the page Properties > RSS (the page must be checked out), and Level 10 users can rebuild feeds from Content > RSS as well. Click the "Rebuild Feed" button, choose which server to publish the XML file to, and click Publish.