Isito routing gives 503 for 1 service

I have 5-6 services and has around 7-8 routes (match uri prefix) mapped to each service hosts added in istio virtual service, out of which 2 services are giving “HTTP ERROR 503” while hitting the domain/(prefix).

Other services are giving 200 response.

While checking the ingress-gateway logs for the non-working URL, there is “-” mentioned after the domain. The same virtual service configuration is working fine for the same service in different environment.

What I am doing wrong here ?

Service A working fine in environment A and same Service A not working in environment B but using same istio virtual service configuration yaml