You can get this error if docker doesn't shut down cleanly. The following answer is for the docker snap package.
Run snap logs docker
and look for the following:
Error starting daemon: pid file found, ensure docker is not running or delete /var/snap/docker/179/run/docker.pid
Deleting that file and restarting docker worked for me.
rm /var/snap/docker/<your-version-number>/run/docker.pid
snap stop docker
snap start docker
Make sure to replace ????<your-version-number>?
with the appropriate version number.