The problem of not correctly recording the last-read message only seems to happen on the mobile skin. i.e. if I last visited a thread in mobile, the next time I go back (whether the next visit is mobile or desktop) often I find it did not correctly record that I already saw those messages and it shows me a bunch again.
On the other hand if my last visit to a thread was on desktop, I have never noticed a problem where the next subsequent visit to that thread starts from the "wrong" message.
There is no one thread to give you -- this happens widely across all threads and all forums that I follow on FT. So I don't think it's like a database issue where a particular thread gets messed up (as sometimes happens following a merge)
All I can say is, if you use mobile skin with any frequency, and your primary method of reading FT is by following subscribed threads, you will notice this issue. My starting point on mobile is usually:
https://www.flyertalk.com/forum/subs...n&folderid=all