I have the same problem here but my error is different. xf86OpenConsole: Cannot open /dev/tty0 (No such file or directory)
>From what I've read it's caused by Debian not providing correct systemd files and thus breaking Xorg's "unprivileged mode". Before "upgrading", I could startx/xinit as a user no problem. After "upgrading", no. It only works when using sudo or as root.
