I'm not familiar with Traefik and Docker, but I do use Traefik with Kubernetes. One thing you might want to try is making sure you set the scheme that Kibana uses, as I believe by default, even if you are using an https entrypoint, Traefik will still try to send the connection to an http backend.
Here is a Kubernetes example (it's not a 1-to-1 match, but should help)
- kind: Rule
- kind: Service
scheme: https #<----- Scheme set here to https (as Kibana is setup to uses https instead of http)