Facebook changed the story_fbid query param recently, which we use to generate item ids. It now changes regularly, so our ids change, so the same post(s) keep reappearing in feeds and consuming readers as if they were new.

Key point is that story_fbid values now start with a pfbid prefix, followed by a 67-char base64 string. Redacted example URL:

https://www.facebook.com/story.php?story_fbid=pfbid02X2rBJGbjbvzeJSC8ifzkpmXbULz...&id=542442336

(id here is a Facebook user id; it hasn't changed.)