The same for me: this worked before in Ubuntu GNOME 16.04, and for me bug appeared in Ubuntu 18.04. The extension mentioned by @david23 works for me as a workaround.
-- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1743736 Title: In overview, windows from all workspaces are shown for the second display (when using "Workspaces span displays") To manage notifications about this bug go to: https://bugs.launchpad.net/gnome-shell/+bug/1743736/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs