What does DC response code mean from envoy in istio ingress pod

I am using Istio 1.6.2 with mTLS enabled.
I am using istio ingress pods.
I have a service, lets call Foo

Users can access Foo service via Istio Ingress.

I am getting random Foo service call failure with “DC” response flag from envoy, when i check logs of istio-ingress pod.

Foo service is healthy and nothing seems to be wrong in the logs.

What could be wrong. Need expert help here.