Regarding the linked thread, a Frater posted in the thread a few hours ago but the post was removed because more than 90 days have passed since the last active post before it and the post added nothing of value to the overall conversation. That is why you received an e-mail notification but then found no new post.
Regarding your second point, that happens when posts have been removed in the thread. The e-mail is sent with the correct post ID number but since the post has since been hidden, it will redirect you (following whatever parameters) to another post, mostly probably the last one you read in the thread.
'Perfer et obdura, dolor hic tibi proderit olim.' - Ovid
Chronic procrastinator & amateur "butterfly hobbyist".