"Cannot create service: subset not found" providerName=kubernetes

I'm trying to run Eclipse Che on my selfmanaged K3s-cluster, which has Traefik 2.2 installed. I configured Eclipse Che to use custom Ingress Annotations as follows:

annotations:
    kubernetes.io/ingress.class: traefik
    traefik.ingress.kubernetes.io/router.entrypoints: websecure
    traefik.ingress.kubernetes.io/router.tls: "true"

However, the ingresses are not picked up by Traefik, and produce the error msg="Cannot create service: subset not found" providerName=kubernetes

How can I troubleshoot this?

For reference, the 4 "static" ingresses that Eclipse Che creates/uses (che-ingress, keycloak-ingress, devfile-registry and plugin-registry) have the same annotations, yet they are working correctly!