On the missing issues page, how do I unhide hidden issues?
It’s not possible to do that there.
To unhide series that you’ve hidden, you have to look them up in Manage Pick Lists screen
(menu top left, then Manage Pick Lists, then Series, then find it and click it and unhide it with the checkbox).
I could, if you want, unhide ALL series for you. There is no tool for it, but I can do it if you want that.