You might want to add the label
- traefik.http.services.ombi.loadbalancer.server.scheme=https
to specify the scheme for communicating with the backend ombi container, as I understand ombi is doing HTTPS right?
Also, if ombi provides a self signed certificate, you might want to skip the tls verify, or better: providing the certificate to Traefik so it can dial with ombi in TLS securely. Both options can be found on https://docs.traefik.io/reference/static-configuration/file/ (clue: check [serversTransport] section 
)