At
https://en.wikipedia.org/wiki/%28%CE%B5,_%CE%B4%29-definition_of_limit
right after I moved the mouse from over one of the reference links [1][2].
{ "errorMessage": "NotFoundError: Node was not found", "url": "https://en.wikipedia.org/w/load.php?debug=false&lang=en&modules=jquery%2Cmediawiki&only=scripts&skin=vector&version=3hR%2F0Nym line 4 > eval", "lineNumber": 108, "columnNumber": 0, "errorObject": {} }
Trying again with debug=1 in the URL, I got
{ "errorMessage": "NotFoundError: Node was not found", "url": "https://en.wikipedia.org/w/load.php?debug=true&lang=en&modules=ext.gadget.ReferenceTooltips&only=scripts&skin=vector&version=06fb8d94e44e&*", "lineNumber": 40, "columnNumber": 0, "errorObject": {} }
so it is actually a problem with
https://en.wikipedia.org/wiki/MediaWiki:Gadget-ReferenceTooltips.js
Reported at
https://en.wikipedia.org/wiki/MediaWiki_talk:Gadget-ReferenceTooltips.js#NotFoundError