There's also a lock icon next to the "App not working" category in the header, which I took to mean that that entire category is hidden from logged-out users (which experimentally seems to be the case).
Obviously, deliberately hiding a negative story on our Discourse is a little like deleting a bad tweet; it's just going to guarantee someone captures and boosts it. We have a lot of flaws! But not knowing how the Internet works probably isn't one of them. No idea what's going on here, still trying to work it out.
Not going to try and guess why or when that tag change happened. Personally, I'm less concerned with this particular thread than with the apparent decision to systematically hide all potentially-negative threads from search engines.
FYI, this doesn't appear to be strictly accurate. The OP commented at 23:52 UTC saying that the thread had been made private, and the reply from "Sam-Fly" was not posted until 02:36 UTC.