This thread can still be read and even posted to, but no longer shows up in my feed.
Hey there, this might be an artifact of that thread being merged (as you can see in the moderator comment). I can't think of an immediate fix, but will file that as a bug for the Tech Team's backlog. Thank you for letting us know!
It looks like the thread may have been "hidden" for some users after the merge. It should be possible to add it back to your feed by clicking the button to show hidden threads, then un-hiding it. Let us know if you run into any other issues.
Worked for me, thanks!