One more small (I think) bug:
This cluster of stories came first in my feed:
As I scrolled, each was marked read. I’ll call this group A.
Later down in the folder, the article appeared again, say group B.
The primary group B story was already marked as read since it appeared as story A1. Primary A was sorted as B2.
I would personally expect all the stories to be rolled up and appear exactly once. Instead, in my example, the articles will appear 5 times each – once as the primary and four times as a part of the cluster.