This isn't a global issue affecting everyone or we'd be inundated with comments here.
I've just successfully changed worlds via the in game world changer and also via the world selector.
As such, the first piece of advice is to clear your history, cookies and cache on the computer. If that doesn't work, disable all scripts and script enabling programs such as greasemonkey or tampermonkey and try again. Finally, if that doesn't work try a different browser such as Edge, Firefox or Chrome (choose one you don't normally use for the game).