When you are logged in and testing this, are you logged in as an admin or some other user type? If it’s as some other user type then this could be a permission issue with that user type not having access to the post of the custom post type for some reason. I think there have been similar issues posted about that here. If you’re logged in as an admin and seeing this issue then I would start by deactivating other plugins because I cannot reproduce this problem on a test site with only ACF installed.
