The Restricted navigation setting should do what you want: allow people to click the Menu to jump to previously viewed slides, but not let them advance. What you're describing sounds like Locked navigation: a person can't use the menu to jump around.
I suggest you double-check the navigation setting, in case you accidentally selected Locked.
If it is set to Restricted, yet it's not allowing backward movement, that's what is politely called "unexpected behavior." You can submit a case directly to the Articulate staff here: https://access.articulate.com/support/contact