Did you notice the stickies missing from the main Discussion page?
We are running a little test that removes sticky threads from the combined forum view after the post has been up for a while. So instead of always seeing the same stickies when you click on "Discussions", you will only see the latest and freshest ones, and also way more new posts from the forums you subscribe to, without having to scroll forever to do so. This also means that your posts have a chance of being more visible.
(read full announcement in this forum post)