User blog comment:Rappy 4187/Technical Update: March 10, 2015/@comment-452-20150312181303/@comment-452-20150313201307

Yes, I understood that. My test wikis also have no-one in the chat.

One other thing that you may or may not be aware of is that both Chat.js and the welcome message are cached, so you might be better off testing on a fresh wiki.

Since you mention that the issue is related to chat hacks, it obviously doesn't occur on all wikis, as not all wikis have that enabled. Feel free to enter http://452test.wikia.com/wiki/Special:Chat - No scripts are loaded there by default, so it should work fine for you.

Edit: Good idea checking the loaded scripts via the networking tab. inspector. I personally found the networking tab useful when debugging this yesterday because I could see when each scripts was loaded.