Thank you for the answer and the reference to personal responsibility here in the forum :-) This is very relevant, and my post was not very clever. Here is why:
As I am relatively new to docker (sic!), specially in a complex setup with mailcow, there is still some uncertainty on the subject of Docker. I am not always sure what is what.
I saw the thread about containerd already, but was unsure if it is really related to the observation.
I checked meanwhile which container is causing the error message. It is mailcow-dockerized_dockerapi-mailcow_1 and mailcow-dockerized_dockerapi-mailcow_2. All other containers do not cause any error message in the journal by docker stats <containerid>.
What do you think? Is it still related to docker/containerd? Or is it something with the mailcow setup after all?
containerd.io-1.5.11-3.1.el8.x86_64
Docker version 20.10.14, build a224086
Mailcow 2022-04(Moopril)