We have a configuration where we have multiple routes for the ingress-gateway with different hostnames.
When you accidentally create two gateways listening the same hostname, it causes that all the gateways in the mesh stop working. Even the ones which are not listening that hostname.

For example:

apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
name: foo-gateway
spec:
selector:
istio: ingressgateway
servers:

• hosts:
• foo.bar.com
  port:
  name: http
  number: 80
  protocol: HTTP

and they you create new gateway with the same hostname:

apiVersion: networking.istio.io/v1alpha3
kind: Gateway
metadata:
name: foo2-gateway
spec:
selector:
istio: ingressgateway
servers:

• hosts:
• foo.bar.com
  port:
  name: http
  number: 80
  protocol: HTTP

This will cause that all the gateways stops working and the ingress-gateway routes will response with http code 503.