On the 'recent posts' page the link is:
but the link in the email is:
If the new reply isn't on the first page of the thread, without the '?page=2' part in the url you get sent to the top of the first page instead. This bug happens sometimes if someone pastes a link to a specific post in a thread, but they've changed their 'posts per page' higher than the default - such that the post is on their first page, but not anyone else who's still using the forum default of 50.
Similarly, if you went into your profile and changed the number of posts per page to 1000, the links in the notification emails would work correctly.