Out of 739 articles checked, the Facebook numbers were coming back for almost none of them. Two separate causes, both fixed.
Trending RSS ranks articles partly by how much they are being shared on Facebook. That signal was arriving empty for nearly every link, which quietly made the whole ranking worse without ever looking broken.
Two causes. First, we were asking Facebook about URLs that still carried tracking parameters, which Facebook treats as different URLs from the ones people actually shared. Those get stripped now. Second, our own rate-limit protection was cutting off the remaining batches whenever one hit a per-URL limit, killing about 80% of perfectly usable requests.
Requests are also batched now, up to 50 links per call, so a run that used to make 800 calls makes about 16.
Signal tracking was covering five days. It is 24 hours by default now. This is a trending tracker, and half of every run was being spent on two to five day old articles that had long stopped moving. If you want the longer window back, it is a setting.