On Ubuntu focal

docker: Error response from daemon: failed to create shim task: OCI runtime create failed: runc create failed: unable to start container process: error during container init: unable to apply apparmor profile: apparmor failed to apply profile: write /proc/self/attr/apparmor/exec: no such file or directory: unknown.

Maybe installing the package "apparmor" helps...

This is not a bug of the relay software, but it affects the latest Docker Engine version. I think the relay operators will be able to handle it.