GGV2: Unable to run docker containers: docker.sock - permission denied

This was working just fine a month ago, but now:

=> When Greengrass tries to install docker images with "docker load -i [...]" I get this error:
2021-04-14T15:24:51.673Z [WARN] (Copier) xxxxxxxxx: stderr. Got permission denied while trying to connect to the Docker daemon socket at unix:///var/run/docker.sock: Post http://%2Fvar%2Frun%2Fdocker.sock/v1.24/images/load?quiet=1: dial unix /var/run/docker.sock: connect: permission denied. {scriptName=services.xxxxxxxxx.lifecycle.Install.Script, serviceName=xxxxxxxxx, currentState=NEW}
2021-04-14T15:24:51.676Z [WARN] (pool-2-thread-17) xxxxxxxxx: shell-runner-error. {scriptName=services.xxxxxxxxx.lifecycle.Install.Script, serviceName=xxxxxxxxx, currentState=NEW, command=["docker load -i /greengrass/v2/packages/artifacts/xxxxxxxxx/1...."]}

I tried:

• reverting back to Nucleus 2.0.3 but I seem to get the same problem.
• The only thing that solves it, is to make the docker.sock world-writable... but that is not going to production.

More info:

• Greengrass is running as root.
• I can run these commands myself with no problem in a shell
• privileged containers I spin up can access the docker.sock with no problem
• This happens both in my arm and amd64 devices

I don't know how to check in what user does Greengrass try to run the docker load command, but I assume it is its own user.

Has anyone experienced something similar?
I feel silly asking this question because it was working before, but I did not change anything so I am confused.