Custom docker bridge network - containers still only connect via serverip:port not hostname

Hey guys,

As the title suggests, I simply cannot use http//containername:port to connect to other containers. I always have to use http://serverip:port. This happens regardless of whether I'm running docker containers from the app store, or whether I'm running compose stacks in portainer. I have made sure that the containers are on the same custom bridge network (see attached pictures), but still no dice. While things work fine with http://serverip:port, it is annoying. I also can't use the custom bridge ip assigned to each container to connect to others, it's always the serverip. Any ideas?

Thanks

compose.yml