There is no way to access the Switch role option under the "Essential" theme either, but an upcoming update will hopefully fix this.
Why was this option moved?
We are using custom theme too. And we noticed that the "switch" role has been moved.
Is there any specific reason it was moved away from the regular menu into top menu? I think we will have a workaround which just add the link to the "switch role" page somewhere in the page. Most probably we will add it as a regular menu item (should end up something close the earlier version where it was in the menu). Has anyone done it? Any suggestions about that? I'm mostly concerned whether I can modify the menu from theme.