Comment 1 for bug 1882942

Adding set -x to the postinst section, we see this:
Setting up docker.io (19.03.11-0ubuntu1) ...
+ modinfo zfs
+ zfs mount
+ + awkcut -d/ -f1
 $2=="/" {print $1}
+ rpool=rpool
+ [ -n rpool ]
+ findmnt -n -o SOURCE /var/lib/docker
+ dockermnt=rpool/docker
+ echo rpool/docker
+ grep -qE ^$|/ROOT/
+ dpkg --compare-versions 19.03.8-0ubuntu1 le-nl 19.03.8-0ubuntu2
+ mv /var/lib/docker.migrating/* /var/lib/docker/
mv: cannot stat '/var/lib/docker.migrating/*': No such file or directory
dpkg: error processing package docker.io (--configure):
 installed docker.io package post-installation script subprocess returned error exit status 1
Errors were encountered while processing:
 docker.io