I have a couple of tag RSS feeds set up across multiple sites, and apparently starting on January 2nd, occasionally the feeds are fetching data for a completely different tag.
For example, on January 2nd, the cics tag feed (https://stackoverflow.com/feeds/tag?tagnames=cics&sort=newest) fetched a number of questions tagged with github-api. An hour or so ago, the zos (https://serverfault.com/feeds/tag?tagnames=zos&sort=newest) tag fetched a number of questions tagged with github-api as well. This isn't repeatable, exactly, because when I've fetched the tag manually, the resulting XML doesn't have any of these questions in them, but they show up in my feed reader.
mcapreturned a bunch of results that seemed to be related towix.kedrofeed of Stack Overflow.