Some posts may not appear in your feed for a few common reasons. In many cases, a feed delay is active and the post is still within that delay window, so it has not yet been included. It is also possible that caching (for example via a WordPress cache plugin, server cache, or CDN) is still serving an older version of the feed. In addition, another plugin may be overriding or modifying the feed output.

To troubleshoot this, please follow these steps:

1. Check your feed delay settings to make sure the post should already be visible.
2. Verify that the post is assigned to the correct categories that your feed is using.
3. Clear all caches (WordPress cache, server cache, CDN) and then reload the feed.
4. Temporarily disable other RSS-related plugins to see if one of them is interfering with the feed output.