I had this same question shortly after I first started posting here. I ended up PMing an admin, and got this response back:
“Can’t help you, its broke. We will get a new forum before we fix this one.”
…Which actually seems to be the default response to just about any inquiry or request made around here. Forget the fact that most everyone still uses this forum, and isn’t migrating over to the new one for a reason.
So, the solution I conceived was to use bookmarks instead. And to make sure I got all the favorites I had already saved (as of course, there’s no way to figure out it’s broken until you have saved posts that you can’t see), I just bookmarked each favorite and then deleted it from the favorites list. As the list got shorter, all the older favorites you can’t view come to the front page, so you can see them. I realize it’s a local solution and means you can’t view your favorites from just anywhere you log in, but still. Better than nothing.