Duplicate listener 0.0.0.0_8081 found

Networking
1

Versions:

Istio: v1.7.3
Knative: v0.20

Issue:

After deploying knative serving v0.20, it adds a service knative-local-gateway that use 8081 as a targetPort and now we have a warning on istio-ingressgateway as shown below:
listener(s) 0.0.0.0_8081: duplicate listener 0.0.0.0_8081 found

More details:
we deployed istio and knative in two different clusters with the same configuration but we have different resulrts:
cluster 1 with the warning:
ADDRESS PORT MATCH DESTINATION
0.0.0.0 8081 ALL Route: http.80
0.0.0.0 15021 ALL Non-HTTP/Non-TCP
0.0.0.0 15090 ALL Non-HTTP/Non-TCP

cluster 2 :
ADDRESS PORT MATCH DESTINATION
0.0.0.0 8080 ALL Route: http.80
0.0.0.0 8081 ALL Route: http.8081
0.0.0.0 15021 ALL Non-HTTP/Non-TCP
0.0.0.0 15090 ALL Non-HTTP/Non-TCP

Any advice on troubleshooting this issue would be greatly appreciated.