just checked my unread posts, and again software v idiots and fastest were in the list, both with different last posters.

read software, then clicked show all unread posts, and fastest has disappeared.

In my case the ones I lose are, as far as I can tell, always in the same section.
Just did a few tests. I picked on a section e.g. "Layout Construction" and made a list of all the unread posts. After viewing one of the posts I went back to the unread list and as expected the one I had just read was gone but so was another that I hadn't.
I repeated this with other sections and about 50% of the time the same thing happened.

A good tip that I've said before, but may only be useful on certain devices, is to select the thread to open in a new tab/window - which would leave the original tab/window untouched without loss of threads to read.

still happening ...

checked 'all unread posts'

1 x angry thread
1 x unhappy thread

read angry thread

back

oops, unhappy thread had disappeared.

found it on the list under forum.

I know I'm slow but I've just discovered today some posts slip through the net. Bearing in mind I'm on the forum at least twice a day and use the 'Show all unread posts'. This can be annoying, especially as a couple today were in a thread I started!