So, it appears that
this thread in the Air Canada forum was split off from this one in the Delta forum:
The thread perpetually shows up in MyFlyerTalk despite having viewed the very last post multiple times, and the "Go to First New Post" button (blue arrow inside a box) links to the thread split off and moved the Air Canada forum.
I checked the thread in the Air Canada forum, and I am NOT subscribed to the new split off thread, so there's some sort of bug where the button takes me to the wrong thread.
I have tried unsubscribing from the thread in the Delta forum, and then resubscribed, which does not fix the issue, as the thread immediately reappears in MyFlyerTalk and still links to the split off thread.