Specific Virutal server log to Splunk - not working

Yes, I did capture the traffic, In non-working scenario there is a reset from Virtual server to the client and BigIP is not sending traffic to the backend servers. See the pic attached.

10.37.21.185 is client IP and 172.27.129.82 is the virtual server.

Here is the iRule:

when CLIENT_ACCEPTED {
  set client_address [IP::client_addr]
  set vip [IP::local_addr]
  set splunk_pool SPLUNK-HSL-POOL
  set hsl [HSL::open -proto UDP -pool $splunk_pool]
}
when HTTP_REQUEST {
  set http_host [HTTP::host]:[TCP::local_port]
  set http_uri [HTTP::uri]
  set http_method [HTTP::method]
  set http_version [HTTP::version]
  set virtual_server [LB::server]
  set http_user_agent [HTTP::header "User-Agent"]
  set http_content_type [HTTP::header "Content-Type"]
  set tcp_start_time [clock clicks -milliseconds]
  set req_start_time [clock format [clock seconds] -format "%Y/%m/%d %H:%M:%S"]
  if { [HTTP::header Content-Length] > 0 } then {
  set req_length [HTTP::header "Content-Length"]
  } 
  else {
  set req_length 0
  }
}
when HTTP_RESPONSE {
  set res_start_time [clock format [clock seconds] -format "%Y/%m/%d %H:%M:%S"]
  set node [IP::server_addr]
  set node_port [TCP::server_port]
  set http_status [HTTP::status]
  set req_elapsed_time [expr {[clock clicks -milliseconds] - $tcp_start_time}]
  if { [HTTP::header Content-Length] > 0 } then {
  set res_length [HTTP::header "Content-Length"]
  } 
  else {
  set res_length 0
  }
  set hsl [HSL::open -proto UDP -pool $splunk_pool]
HSL::send $hsl "<514> HSL, CLIENT_IP=$client_address, VIP=$vip, VIP_NAME=\"$virtual_server\", 
    SERVER_NODE=$node, SERVER_NODE_PORT=$node_port, HTTP_URL=$http_url, HTTP_VERSION=$http_version, 
    HTTP_STATUS=$http_status, HTTP_METHOD=$http_method, HTTP_CONTENT_TYPE=$http_content_type, HTTP_USER_AGENT=\"$http_user_agent\", 
    HTTP_REFERRER=\"$http_referrer\",REQUEST_START_TIME=$req_start_time,REQUEST_ELAPSED_TIME=$req_elapsed_time, BYTES_IN=$req_length, 
    BYTES_OUT=$res_length\r\n"
}