Yes, you are right. The tty is working, but the display does not change.
I pressed ctrl + alt + f1. I still saw my browser. I signed on blind and tried sudo reboot also bind.
And it works well. 
Nice to know, but for the future a little uncomfortable.
sudo chvt 1 has the same effect. So the tty’s are working. I looked at the log and lightdm log also, but there is nothing unusual to find.