Traefik uses the lowest port number by default when auto-discovering services, however that also implies that it will try to bind to UDP ports that do not make any sense in terms of web-services. In order to work around this shortcoming, labels can be added that will specify the port that traefik should route the traffic to.
For example:
-l traefik.http.services.jellyfin.loadbalancer.server.port=8096 \
will route incoming traffic to the traefik host to port 8096 for this service. This line was taken from a Jellyfin setup with Jellyfin running on port 8096.