Some development snapshots of Ubuntu 20.04 (Focal Fossa) had an incorrect seed.yaml file and this can lead to a bad experience during the Debian package upgrades of snapd.
We will issue a warning via snapd on these systems and we are also working on an automatic fix.
If you see the warning on an affected system, a workaround is to:
mv /var/lib/snapd/seed /var/lib/snapd/seed.disabled