Traefik Ingress does not necessarily rely on certificate / secret from the same namespace but can rather end up using certificate from another namespace. So copying the same certificate to multiple namespaces (with e.g. emberstack reflector) is unnecessary and misleading. Read more here: Documentation: clearly document Kubernetes Ingress Class namespaced tls certificate misconception · Issue #12116 · traefik/traefik · GitHub.
Hence I have a question. What is the recommended way to use the same TLS Certificate in Ingress'es from multiple namespaces? Maybe @bluepuma77 
PS another attempt to get an "official" answer for How to use the same wildcard TLS certificate in multiple IngressRoutes in different namespaces? from @Kitanotori
