Envoy Proxy HTTP 503 Connection Local Reset error

Question

I'm using envoy proxy as a reverse proxy in a container for my loadbalanced application. We recently had a network outage which caused envoy proxy to return 503 to our downstream clients. Normally, when the network outage recovers, envoy proxy will be able to connect to our upstream servers properly again and everyone is happy.

However, after the network outage recovers, the downstream clients are still receiving HTTP 503 with LR response flag unless I restart the containers. Am I missing something? Can someone point me to the right direction on how should I resolve this issue?

admin:
  access_log_path: /tmp/admin_access.log
  address:
    socket_address:
      protocol: TCP
      address: 0.0.0.0
      port_value: 9901
static_resources:
  listeners:
  - name: listener_0
    address:
      socket_address:
        protocol: TCP
        address: 0.0.0.0
        port_value: 10000
    filter_chains:
    - filters:
      - name: envoy.filters.network.http_connection_manager
        typed_config:
          "@type": type.googleapis.com/envoy.config.filter.network.http_connection_manager.v2.HttpConnectionManager
          stat_prefix: ingress_http
          server_name: none
          route_config:
            name: local_route
            response_headers_to_remove:
            - x-envoy-upstream-service-time
            virtual_hosts:
            - name: local_service
              domains: ["*"]
              routes:
              - match:
                  prefix: "/"
                route:
                  host_rewrite: api.example.com
                  cluster: service_api
          http_filters:
          - name: envoy.filters.http.router
          access_log:
          - name: envoy.access_loggers.file
            filter:
              not_health_check_filter: {}
            config:
              path: "/dev/stdout"

  clusters:
  - name: service_api
    connect_timeout: 30s
    type: LOGICAL_DNS
    dns_resolvers:
      socket_address:
        address: 127.0.0.1
        port_value: 53
    # Comment out the following line to test on v6 networks
    dns_lookup_family: V4_ONLY
    lb_policy: ROUND_ROBIN
    upstream_connection_options:
      tcp_keepalive: {}
    load_assignment:
      cluster_name: service_api
      endpoints:
      - lb_endpoints:
        - endpoint:
            address:
              socket_address:
                address: api.example.com
                port_value: 443
    transport_socket:
      name: envoy.transport_sockets.tls
      typed_config:
        "@type": type.googleapis.com/envoy.extensions.transport_sockets.tls.v3.UpstreamTlsContext

Any pointers will be much appreciated.