Board Thread:Support Requests - Getting Technical/@comment-5693502-20151117192627/@comment-4018164-20151117193158

Delete MediaWiki:Chat-welcome-message in your wiki. This extra bit was how MediaWiki:Chat.js and MediaWiki:Chat.css were originally imported (now they are imported by default so there's no point in keeping it). Anyway, since now you can no longer add HTML to MediaWiki pages for chat, it is displayed as plain text instead of being rendered. Deleting the page should change it back to its default wikitext and solve this issue.