User blog comment:BertH/Technical Update: March 2, 2016/@comment-5275700-20160303014235/@comment-1251315-20160303121343

@Ckwng The 404 happens if the menu is opened too quickly before the page is completely loaded. Every time I waited for the page to fully load, no issues occurred. To me, Wikia should make it so that the alerts button is not usable until the page is completely loaded (aka "document.ready") to work around the bug.