I have had to manually link the subforums for all my purchases for awhile now.
Dunno if they just stopped doing it or if it stops after you have so many checked.
Yes, I've noticed this happening for a while now - new library purchases not automatically adding themselves to your community forums lists anymore, meaning you have to "show all" games and manually check the boxes to add them yourself.
Think it happened back when the website had a design tweak - some time ago now - and I just presumed they'd get around to fixing it soon. Apparently not, because I bought the Archives Collections yesterday and just had to add this
forum manually :)