Subforum Access Premissions

Is there a way people outside my game can view the threads in my game’s subforums?

There is a lot of content there I would have liked prospective players to peruse, but it looks like the subforums are inaccessible to them, and I had to move all my threads to my public forum (thereby creating a horrible clutter)

I can see the subforum threads in your public Masks game, though not in the Karameikos one.
You can try checking the Administrative Control Panel and compare what's different in two games? You can access ACP when viewing the game forum, there is a link on top right above the list of subforums. (Which you probably know since you have subforums, oops; but I'm pretty sure that if it's a permission issue and not a bug, it's probably in here?)

I set up the permissions in the exact same way. Could this be a bug?

It might be; I don't think I've ever seen this problem before. :0 Probably worth reporting it to Keleth or vagueGM.