I experienced this as well within a VM running Ubuntu 19.10. I have an Nvidia GTX 1060 card. I started the upgrade process to 19.10 and mid way the screen went blank with only a blinking cursor. Rebooted the machine and I was greeted with the login page, but when I logged in there was a screen that said "something went wrong" and logging out started the process again.
Rebuilt the VM and this time disabled Automatic login before starting the upgrade. The upgrade went flawlessly and finished.
I experienced this as well within a VM running Ubuntu 19.10. I have an Nvidia GTX 1060 card. I started the upgrade process to 19.10 and mid way the screen went blank with only a blinking cursor. Rebooted the machine and I was greeted with the login page, but when I logged in there was a screen that said "something went wrong" and logging out started the process again.
Rebuilt the VM and this time disabled Automatic login before starting the upgrade. The upgrade went flawlessly and finished.