Glad you figured it out! A separate network for a set of services that need to talk to eachother is the way I do it for my selfhosted tools, if you want some more ideas on setting up the *arr apps using docker compose, this is my current setup: https://github.com/hosaka/selfhosted/blob/main/servarr.yml

I think you’re using docker internal IPs, which are not static and can change between docker compose runs. You can instead address them by name if you connect then to a same virtual network: https://docs.docker.com/compose/networking/#specify-custom-networks

This allows two service to “see eachother”. For example “calibre:8081” will resolve to an internal IP address. I’m general, this is a better approach when you need to connect apps to each other.