This is showing up in production logs in wikidata.org on Vector. Possibly relates to T217726 ?
at getFormData URL1:17:501 at specialRenderFunction URL1:19:915 at special/< URL1:4:843 URL1: https://www.wikidata.org/w/load.php?lang=en&modules=jquery.highlightText%2Csuggestions%7Cmediawiki.searchSuggest&skin=vector&version=1rlio