If it helps, I just disabled the BB Classic plugin (which I need until MediaPress updates to BB12 compatible. With BB Classic disabled, I get a 404 error when I click the Favorites or Subscriptions tab in the Forum section of BuddyPress Profile. I have a funny feeling that the problem with Unfavoriting and Unsubscribing has something to do with BuddyPress trying to create a URL with a redirect for bbPress.
Also, I did this test after updating to BuddyBoss 12.1.1 today. The URL to Unfavorite within the BuddyPress Profile is still with BB Classic enabled:
https://[site-url]/members/admin/forums/favorites/?action=bbp_favorite_remove&object_id=55&redirect_to=https%3A%2F%2F[site-url]%2Fmembers%2Fadmin%2Fforums%2Ffavorites%2F&_wpnonce=f9336f0991
