tldr: for about 30% of pages the infobox doesn't get moved below the lead paragraph
While doing chores, I noticed a spike in first interactive time for the Barack Obama page
Investigating it in wpt (there were no active campaigns) it became quite obvious
As you can see the image showsin one of the runs but not the other.
Visiting https://en.m.wikipedia.org/wiki/Barack_Obama it's clear the first paragraph is not getting moved.
Inspecting the HTML there are two instances of .mw-empty-elt preventing this move
<p class="mw-empty-elt"> </p>
There are no visible spikes in logstash relating to this error as the error logging incorrectly assumes that these empty paragraphs are the lead paragraph but found 3 in 10 articles had the problem.
Visit the following pages on mobile and ensure the lead paragraph shows above the infobox
Visit some random articles and check they also position infobox below first paragraph. Report any violations.
Any "p" with the class mw-empty-elt should not be considered the lead paragraph
Possibly related to some Tidy changes in https://gerrit.wikimedia.org/r/#/c/mediawiki/core/+/295613/