Well, this issue was my pain in the ass until I fully understood what was going on with nginx-proxy container and docker-compose v2.

When you have docker-compose.yml with separate frontend network you need to connect this network to nginx-proxy container in order to work. Obviously, there is no frontend network until you up your containers for the first time!
When you do

docker-compose up

network will be created, but nginx-proxy will not be attached to it! So you need to shut down your app containers, do

docker network connect itservice_frontend-tier nginx-proxy

and then to fire your containers up again! But wait, you need to restart nginx-proxy container to connect to this new network!

As you can see this process can not be single step deployment solution on CoreOS, but now you know why and how to fix this.