Could be a job failure. I don't see anything in logstash that seems relevant, and the edit was > 7 days ago so any jobs we ran have fallen out of the job queue by now.
I ran the job manually from terbium mwrepl with:
(new \CirrusSearch\Job\LinksUpdate( Title::newFromText( 'Q55148401' ), [ 'addedLinks' => , 'removedLinks' =>  ] ))->run();
All worked fine and it updated the page. Not sure why it didn't work the first time around.