The ALT+TAB window switching menu only appears on my primary (laptop) screen, not the screen that is active. The top-bar, where notifications live, is also not-present on my second monitor. Both these behavior are new since in-place upgrade from 17.10.
Any way I can get back the previous behavior?
As of today that window only shows up on your primary monitor.
You can go into "Settings" and make whatever screen you want your primary.
The window will only show up on one screen at a time.
This is the same issue as in: Alt+tab displayed on current monitor in Ubuntu 17.10
The answer appears to be "this is intended behaviour of GNOME 3 and you cannot change it."