Sometimes DNS takes a long time to fully propagate. In order to obtain SSL certificates, Cloudron has to wait for the DNS record (my.domain.com) to resolve correctly to the server's IP before proceeding during setup.
@Felix You can check host my.domain.com on your laptop. Does it give the right IP? If Cloudron is still in the setup page, you can just systemctl restart box on the server and the setup page will come back up.