Dynamic workspaces have stopped working?

I'm not exactly clear when and have no idea why, but at some point in the last couple of weeks, dynamic workspaces have stopped working on 20.10. When I log in, I have only a single workspace and to get anything else, I have to open Gnome Tweaks and configure static workspaces, setting a fixed number of workspaces. Even if I then switch back to dynamic workspaces, I still get the number of workspaces I configured statically.

Has anyone else seen this? I've tried disabling extensions but this makes no difference.