The tag riesz-representation-theorem was created a few days ago. The tag creator added almost immediately after the creation above 60 questions to that tag. And it seems that he continues in his retagging efforts in relatively large batches.
You might notice that you won't see those questions if you choose newest rather than active tab. And if you display the recently active questions on desktop rather then on mobile, you will also see which user caused the most recent activity on the question - which makes the fact that most of them came from the same user immediately obvious.
I will add that stuff like this has been discussed in the past. It is true that the site has grown since those discussion, so probably bumping is less noticeable among many new questions. But still one should try not to bump too many old questions at the same time. (Although different users might have different views on what exactly too many means and the number of admissible edits to old questions is now probably higher - since the site is now bigger.)
Some examples of older post about this - you can find many others, for example if you look at the tags bumping and retagging:
This recent feature request is related to such retaggins sprees: Limit for number of questions where tag can be added by tag-creator soon after the creation of tag.