I get the same behaviuor in 14.04 (page up/down moves left and right). Maybe you should try in a screen-specific forum, or in askubuntu.com, as there is no clear indication of a bug here yet.
** Changed in: screen (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Server, which is subscribed to screen in Ubuntu. https://bugs.launchpad.net/bugs/1769401 Title: 18.04: Getting emacs-style markkeys to work again ? To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/screen/+bug/1769401/+subscriptions -- Ubuntu-server-bugs mailing list Ubuntu-server-bugs@lists.ubuntu.com Modify settings or unsubscribe at: https://lists.ubuntu.com/mailman/listinfo/ubuntu-server-bugs