I run into the same error over and over when I tried up upgrade to 20.04 LTS.
I'm stuck with this LXD Error, can't redo, uninstall or update my system :-/
Error Message:
==> Installing the LXD snap from the 4.0 track for ubuntu-18.04
error: requested a non-existing branch on 4.0/stable for snap "lxd":
ubuntu-18.04
dpkg: Fehler beim Bearbeiten des Archivs /var/cache/apt/archives/lxd_1%3a0.9_all.deb (--unpack):
new lxd package pre-installation script subprocess returned error exit status 1
Fehler traten auf beim Bearbeiten von:
/var/cache/apt/archives/lxd_1%3a0.9_all.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)
Bernhard