upgrade from 18.04 to 20.04 hangs on lvm2 snapshot

[Denny]

When trying to upgrade my Kubuntu 18.04 to Kubuntu 20.04 by running

sudo do-release-upgrade -d

I get at a point where the installer reads:

...
    File descriptor 3 (pipe:[366994]) leaked on vgs invocation. Parent ID 31982: /usr/sbin/grub-probe

...
grub-probe: error: unknown filesystem.
    File descriptor 3 (pipe:[366994]) leaked on vgs invocation. Parent ID 31982: /usr/sbin/grub-probe
...

Found Ubuntu 18.04.4 LTS (18.04) on dev/,apper/kubuntu--vg-snap
Adding boot menu entry for EFI firmware configuration
done
...

At this point the installer hangs for at least 35 min. Killing it and restarting leads to a kernel panic.

This is on a laptop with lvm2, using an lvm snapshot before the upgrade

[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/1887373/+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.]

[Denny (denny-seniazi)]

https://askubuntu.com/questions/1257667/upgrade-18-04-to-20-04-hangs-after-adding-boot-menu-entry-for-efi-firmware-conf

as is apparent from the link, there is at least one other person affected by this.

[Denny (denny-seniazi)]

These are the dpkg processes hanging during the upgrade:

me@PROX15:~$ ps aux | grep dpkg
root 21111 0.0 0.0 24868 14308 pts/7 Ss+ 12:58 0:00 /usr/bin/dpkg --force-overwrite --status-fd 115 --configure --pending
root 21141 0.0 0.0 31500 21100 pts/7 S+ 12:58 0:00 /usr/bin/perl -w /usr/share/debconf/frontend /var/lib/dpkg/info/memtest86+.postinst configure 5.01-3ubuntu2

please tell me if more information is needed regarding this issue.

[Denny (denny-seniazi)]

Killing the offending processes from another terminal, resumed the upgrade which ended with errors.
Running
sudo apt update --fix-missing
and restarting seems to lead to a working ubuntu 20.04. Nonetheless I think this should be fixed prior to 20.04.1.