Comment 2 for bug 1804938

There are no apparmor denials in dmesg.

Looking at dpkg terminal log:

Preparing to unpack .../15-snapd_2.35.5~14.04_amd64.deb ...
Failed to stop snapd.autoimport.service: Unit snapd.autoimport.service not loaded.
Failed to stop snapd.socket: Unit snapd.socket not loaded.
Failed to stop snapd.service: Unit snapd.service not loaded.
dpkg: warning: old snapd package pre-removal script subprocess returned error exit status 5
dpkg: trying script from the new package instead ...
Failed to stop snapd.autoimport.service: Unit snapd.autoimport.service not loaded.
Failed to stop snapd.socket: Unit snapd.socket not loaded.
Failed to stop snapd.service: Unit snapd.service not loaded.
dpkg: error processing archive /tmp/apt-dpkg-install-MqUKcp/15-snapd_2.35.5~14.04_amd64.deb (--unpack):
 new snapd package pre-removal script subprocess returned error exit status 5

It seems that snapd.prerm script doesn't cope with services being not loaded and barfs.