No GUI after Kubuntu 18.04 -> 18.10 Upgrade

[xghost]

Upgrading my (MSI GP72) laptop running Kubuntu 18.04 -> 18.10 (via `sudo do-release-upgrade`), the GUI doesn't show up. You hear the sound of the greeter coming up, but the login screen is never displayed.

I can login using the terminal and use the laptop normally locally or remotely (i.e. I can SSH into it). I've not found any (obvious) error messages in the following log files:

* /var/log/syslog
* /var/log/boot.log
* /var/log/kern.log
* /var/log/nvidia-installer.log

Checking systemctl status lightdm.service shows it's running. Restarting the service makes no difference. I removed/purged plasma-workspace, plasma-desktop, and nvidia-driver-390 packages (and then autoremoved unused packages), rebooted, and re-installed them, to no effect.

A couple of years ago, I was able to fix a similar issue for 16.04 (https://askubuntu.com/questions/838212/ubuntu-16-10-fails-to-boot-in-msi-gp72-laptop/), but I'm stuck on this one.

How can I fix this issue?

Thanks in advance.

PS: I've been using Ubuntu-based distros since 2006, and it's a shame that upgrading ALWAYS breaks something, usually on the display side. I would've hoped that this kind of recurring problem would've been addressed at some point in the last 10+ years... :/

[Ubuntu Foundations Team Bug Bot (crichton)]

Thank you for taking the time to report this bug and helping to make Ubuntu better. It seems that your bug report is not filed about a specific source package though, rather it is just filed against Ubuntu in general. It is important that bug reports be filed about source packages so that people interested in the package can find the bugs about it. You can find some hints about determining what package your bug might be about at https://wiki.ubuntu.com/Bugs/FindRightPackage. You might also ask for help in the #ubuntu-bugs irc channel on Freenode.

To change the source package that this bug is filed about visit https://bugs.launchpad.net/ubuntu/+bug/1801576/+editstatus and add the package name in the text box next to the word Package.

[This is an automated message. I apologize if it reached you inappropriately; please just reply to this message indicating so.]

[xghost (h-k-ghost)]

I don't know what specific package, installed or missing, is responsible for the missing GUI in the laptop, so I can't specify this information. (Presumably, if I new which package was to blame, I wouldn't be having this issue for over a week now.)

[xghost (h-k-ghost)]

Does anyone have any updates or insights regarding this issue? I can't really use my laptop.