The unread page works well if the # of new posts per visit is fewer than 10. After that it gets a bit hard to keep up 🙂
Some newer changes may make the list a little more manageable.
/cc @psychobunny @baris
Thanks for reporting. This should be fixed in 1.13.2. https://github.com/NodeBB/NodeBB/commit/3cca929a889120c089ce508a74ce40789e0c02d0