Go to https://en.wikipedia.org/wiki/Special:Random and press the Edit button until the icon for TemplateWizard doesn't appear in the 2010 wikitext editor. It seems to occur more frequently in Firefox and Edge. Possibly related to T30563 since the console doesn't display any errors.
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Confirmed in Chromium 81 on Ubuntu. It took me only a few tries. I suspect it's a not a browser-related issue, rather some sort of race condition within ResourceLoader, maybe.