Bionic: apt-get install docker-ce always hangs

I've just upgraded a system from xenial to bionic. We were running docker under xenial, so in an attempt to start clean I went through and apt-get purge all the xenial docker packages. I also removed /var/lib/docker as recommended here.

Before I install docker-ce under bionic, I check updatedb and locate / rm any other docker cruft (including package archives in /var/cache/apt/archives/... so I think I'm starting clean).

I also:

• added the new download.docker.com key with apt-key
• put deb [arch=amd64] https://download.docker.com/linux/ubuntu bionic stable in /etc/apt/sources.list.d/docker.list

When I run sudo apt-get install docker-ce docker-cli, my system hangs here:

Preparing to unpack .../5-docker-ce_5%3a19.03.8~3-0~ubuntu-bionic_amd64.deb ...
Unpacking docker-ce (5:19.03.8~3-0~ubuntu-bionic) ...
Setting up aufs-tools (1:4.9+20170918-1ubuntu1) ...
Setting up containerd.io (1.2.13-1) ...
Created symlink /etc/systemd/system/multi-user.target.wants/containerd.service → /lib/systemd/system/containerd.service.
Setting up cgroupfs-mount (1.4) ...
Setting up docker-ce-cli (5:19.03.8~3-0~ubuntu-bionic) ...
Setting up pigz (2.4-1) ...
Setting up docker-ce (5:19.03.8~3-0~ubuntu-bionic) ...
Created symlink /etc/systemd/system/multi-user.target.wants/docker.service → /lib/systemd/system/docker.service.
Created symlink /etc/systemd/system/sockets.target.wants/docker.socket → /lib/systemd/system/docker.socket.

At this point I do a ps -elf and see that there is a docker process running... killing it unhangs the install, but sudo dkpg -a --configure continues to hang.

I'm running bionic with kernel 4.15.0-101-generic.

How can I get docker fully functional on this system?