I'm experiencing this bug as well. I have a a dozen different repositories, and many of them are only sometimes appearing on my feed and RSS Feeds. I have users who rely on this to see changes to software, and they're not appearing, even though the commits are going through and appear on the repository pages.
We've observed a similar lack of newsfeed updates from one of our private repos. The problem started at least 12 days ago, as that was when the first commit was made that didn't reach the newsfeed (either HTML or RSS formats).