Penpot runs fine but tries to reach "redis.x.y" every 10 seconds

Posted the following on github discussions a few days back without seeing the banner pointing to this place.

since last night my penpot instance (previously 1.17, now 1.19) sends a request to redis.x.y every 10 seconds.
I selfhost penpot with docker compose and all containers are up and running. I do not get any errors in the penpot backend log.
Very sporadic it also requests domain.x.y. config.env is set to PENPOT_REDIS_URI=redis://penpot-redis/0 like in the docker compose template.
How do I know its penpot? Well, stopping penpot stops the requests.

Maybe some of you have an idea what got messed up last night.