This is more a how-not-to-do-it than a Whonix issue
Just finished a WS Physical Isolation build on a 4 GB image… the vm started complaining that only 68 MB space are left, so after a full start I decided to shut down and resize the image. Shutting down was not so easy, the vm kept hanging so I shut down via the vmm button.
After adding a few GB and resizing with gparted the vm started nicely but gave me a graphical login, that refused the user user (why?). I rebooted, ctrl-c, whonixsetup and whonixcheck ok, but still no login possible… :-\