This is not a duplicate of Why does the Related question list not always show up? since that explains the normal caching that causes them to not initially show up until a few minutes (or at most an hour) later; these examples are all a few hours old and the related questions still haven't shown up, so it's clearly a bug.
We temporarily disabled this job last night after some changes to the Elastic search configuration. The people working on it didn't want to re-enable it at the end of the day with nobody around to keep an eye on it, so that was postponed and will probably happen later today.
There is a message in our internal chat to the tune of "the users probably won't even notice" – you sure did prove that wrong :)