Gateway httpsRedirect now being 'ignored' - how to verify

I’ve got a pretty simple EKS cluster, with an Istio Gateway defined to redirect http requests on port 80 to https. Was working fine for approximately 5 weeks.
Now http requests are resulting in 404 responses.

I’ve looked through the Pilot Pod’s log for any indication regarding the use of the httpsRedirect with no luck.

Hopefully someone can suggest where to look to confirm this redirect should be functioning. Nothing in the /etc/istio/proxy/* files in the istio-ingressgateway* pod is jumping out at me.
Related to this, the istioctl proxy-config routes istio-ingressgateway-7488fd6597-wl9qn.istio-system -o json is now showing that port 80 is a Blackhole service. Rather than doing the redirect as was working.
curl requests directly to 443 are working fine, get routed to the correct pod & responses are as expected.

Any pointers greatly appreciated. Thanks.