Disappearing docker images in azure compute engine

Can't find anywhere to get help with this (the ai assisted help chatbot really sucked on this one), so I'll try my luck here instead.

I'm using azure compute engine (CE). I need to use several docker images in the compute engine. However, the CE's diskspace can easily fill up, so I put the images into

/mnt/docker

or into

~/cloudfiles/data/

i.e., my /etc/docker/daemon.json looks like this:

{
 "data-root": "/mnt/docker",
    "runtimes": {
        "nvidia": {
            "path": "nvidia-container-runtime",
            "runtimeArgs": []
        }
    }
}

After logging in after some time to the compute engine, I do "docker info", and I can see that it is "Docker Root Dir: /mnt/docker" still allright.

However, when I do "docker image ls", I can only see the default azure CE docker images (ghcr.io/azure/c3, localhost/c3).

So, the azure CE sneakily erases all other docker images. How can this be avoided?