Open a feed, read everything in it, wait for a new unread item to appear, and click “Next unread”. Instead of moving on to either the new item or another feed, it seems to try to load older items from the feed in an attempt to find the unread item - but it’s newer than the currently displayed items, rather than older, so it never finds it and seems to go on forever (or at least until I stop it so it doesn’t hammer your server).
Doesn’t bother me, as it’s trivial to work around, but I guess it could cause unnecessary load.