systemd: User daemons fail to start after after update removed snap
Solution 1:
I had the same problem with missing snapd package and the same errors about failed services. Turns out it was looking for pam modules in /lib/security which doesn't exist on amd64. The same update quirk that has removed snapd has installed systemd:i386 on my 64 bit machine. The fix was to sudo apt install systemd:amd64 systemd-timesyncd:amd64
Please see also on launchpad: https://bugs.launchpad.net/ubuntu/+source/aptdaemon/+bug/1903273