The problem may exist in older installations. There was no network setting in docker-compose.override.yml for the traefik_certdumper container. By default, docker creates a new network named mailcowdockerized_default. The script enumerates networks named mailcowdockerized and looks for containers that are not there.
Solution:
A line should be added for traefik_certdumper.
network_mode: none
