hey, this problem was introduced by this pr: https://github.com/RocketChat/Rocket.Chat/pull/15204 …
Since the version 2.0 we started to use dynamic imports, the main reason is reduce the load/parse timing on the client side… the problem is: meteor uses the ROOT_URL to fetch the dynamic bundles, so if you misconfigured the url the client will fail to fetch the setup wizard bundle…
I made this fix https://github.com/RocketChat/Rocket.Chat/pull/15432 as a workaround that try to fetch the bundle again using the relative url… but you probably should set this setting in a properly way