all the containers change IP addresses frequently. For home assistant a static IP address of the proxy manager is mandatory in order to reach it. For jellyfin it is useful to see which device accesses jellyfin. If the IP always changes, it doesn’t work properly.
How do I fix a container IP with podman compose (or docker)
You need to create and specify a docker network to get different compose stacks to talk together directly. Default networks are separated between stacks, and have to bounce out to the host and back in, hence are only able to use the exposed ports of the target stack.
You can also specify the IPs that individual services use inside that network if you wish, but docker should handle name resolution within a network.