Docker jenkins ssh-agent "not running inside container" in Ubuntu 22.04

Hi!
Now that Ubuntu 22.04 is released I did a clean install on one of our jenkins-workers to test it but I can’t get the docker ssh-agent to work properly. It can no longer identify that it’s running inside a container, so whenever a job is launching that uses docker I can see in the console “Jenkins-worker-X does not seem to be running inside a container”, followed by the pipeline failing.

I know from before that jenkins uses cgroup information to detect whether it’s running in a container, so e.g. executing cat /proc/self/cgroup in a container should result in a list of lines ending with /docker/<container-id>, which is then used by Jenkins to detect the container. However, once I installed Ubuntu 22.04 the cgroup information no longer contains the /docker/<container-id> which causes the jenkins agent to think it’s running on bare metal.

Even executing the official image has the same problem, i.e. docker run jenkins/ssh-agent:jdk11 followed by docker exec <container-id> cat /proc/self/cgroup ends up with a list without the container hashes on my machine.

How do I troubleshoot this? Has something changed from Ubuntu 21.10 to 22.04 that causes this problem? Is some extra configuration necessary?

Any help would be appreciated!

EDIT: I now realized that the same thing happens in 21.10 if you upgrade all packages to the latest version (and use the latest jenkins/ssh-agent image), so the cause might be in one of the upgraded packages.