If you went to Unread, then used the Dismiss button at the top-right, expecting to mark all the old topics as read, it turns out it also mutes those topics (update: But only if you click the checkbox inside the confirmation dialog, which makes it mute in addition to marking as read).
I did this myself, and also suggested doing it in another thread without realising.
If you did the same, or followed my bad advice, you can undo it as follows:
- Going to your list of muted topics
- Select everything via the = button top-left of the list
(Note that it only selects as much as you have srolled into view, so you either need to scroll a lot, or refresh later and repeat the steps.)
- Click the spanner on the top-right
- Click Change Notification Level and set it to Normal or Watching or whichever you want.
- Do a full F5 refresh afterwards, since the page starts showing you latest topics, not muted topics, after making a change.
F5 Refresh the list afterwards to see if anything is still muted, and repeat until fixed.