Istio virtualservice appendHeaders field in HTTPRoute not working (Istio v1.0.6)

I am trying to send a custom header from the virtualservice to my destination service using the appendheaders field (https://archive.istio.io/v1.0/docs/reference/config/istio.networking.v1alpha3/#HTTPRoute) in the virtualservice manifest yaml but that does not seem to work in Istio 1.0.6.

Is there a workaround to send custom headers to the destination service?

More details below:

apiVersion: networking.istio.io/v1alpha3
kind: VirtualService
metadata:
  name: test-vs-https
  namespace: myns
spec:
  gateways:
  - gateway-mygw
  hosts:
  - host.custom.net
  http:
  - appendHeaders:
      my-custom-header: "true"
    match:
    - port: 443
    route:
    - destination:
        host: test-service
        port:
          number: 443

Gateway manifest below:

apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
  name: gateway-v2deployme
  namespace: v2deployme
spec:
  selector:
    istio: my-ilbgateway
  servers:
  - hosts:
    - host.custom.net
    port:
      name: http
      number: 80
      protocol: HTTP
  - hosts:
    - host.custom.net
    port:
      name: https
      number: 443
      protocol: HTTPS
    tls:
      mode: SIMPLE
      privateKey: /etc/istio/my-ilbgateway-certs/tls.key
      serverCertificate: /etc/istio/my-ilbgateway-certs/tls.crt

The secret was created as a self signed certificate generated from the mtls-go-example (https://archive.istio.io/v1.0/docs/tasks/traffic-management/secure-ingress/#configure-a-mutual-tls-ingress-gateway) using command:

kubectl create -n istio-system secret tls my-ilbgateway-certs --key host.custom.net/3_application/private/host.custom.net.key.pem --cert host.custom.net/3_application/certs/host.custom.net.cert.pem

And I have verified that the ilbgateway service deployment has the right volumes mounted and the secret name matches my-ilbgateway-certs

The destination service does not receive the custom header (verified from tcp dump).

It appears that the main issue was that the https virtualservice was not getting invoked at all. The appendHeaders does work from the http virtualservice.