It is an expected behaviour. Since you are logged in to the site you can not see the Register/Activation page.
Please try opening the link in a new browser or incognito mode where you are not logged in to that site and they will open.
Hope it clarifies.
Sorry, when I said ‘only the Login or Logout menu items show’ I thought it would be apparent that I meant that the Register link doesn’t appear on the menu whether I’m logged out or in.
So, to be clear, I have added ‘Login’ and ‘Register’ to the default menu from the ‘Logged out’ Buddypress section, and ‘Logout’ to the default menu from the ‘Logged in’ Buddypress section.
When I am logged in ‘Logout’ shows in the menu.
When I am logged out ‘Register’ does not appear in the menu, only ‘Login’ does.
As they were both added to the same menu from the same section of the ‘Add to menu’ options this can’t be expected behaviour surely.