I’m seeing the same thing, though it works if I go via the “media” tab on the menu, it’s just in posts and pages it doesn’t work.
I hid the Yoast UI until they can get an update out, but it sure would be nice if that was soon.
I’m wrestling with the problem of a multisite network I’d like to share a sidebar in myself.
Wondering if it’s somehow possible to override the sidebar call so that it forces it to pull widgets from one specific site on the network?