My R6400v2 does not respond to UPnP SOAP call GetTotalBytesReceived

Hello,

my R6400v2 router does not respond to the calls on the UPnP SOAP service "WANCommonInterfaceConfig":

GetTotalBytesReceived, GetTotalBytesSent, GetTotalPacketsReceived, GetTotalPacketsSent

A Python upnp script on the Home Assistant system is getting an error that server is disconnected:

2021-05-13 00:15:14 DEBUG (MainThread) [async_upnp_client.traffic.upnp] Sending request:
POST http://192.168.0.1:5000/Public_UPNP_C2
SOAPAction: "urn:schemas-upnp-org:service:WANCommonInterfaceConfig:1#GetTotalBytesReceived"
Host: 192.168.0.1:5000
Content-Type: text/xml; charset="utf-8"
Content-Length: 292
<?xml version="1.0"?><s:Envelope s:encodingStyle="http://schemas.xmlsoap.org/soap/encoding/" xmlns:s="http://schemas.xmlsoap.org/soap/envelope/"><s:Body><u:GetTotalBytesReceived xmlns:u="urn:schemas-upnp-org:service:WANCommonInterfaceConfig:1"></u:GetTotalBytesReceived></s:Body></s:Envelope>

2021-05-13 00:15:16 ERROR (MainThread) [custom_components.upnp] Error requesting R6400v2 (Gateway) data  Server disconnected

A Windows UPnP client https://www.softpedia.com/get/System/System-Miscellaneous/Universal-Plug-and-Play-Tester.shtml 

 doesn't get any readable response/status either:

There has been a debugging attempt at this issue in the Home Assistant community, but the problem is supposedly in the router side:

https://github.com/home-assistant/core/issues/47914

Has anybody run into this and is there a fix for this issue?

Could my configuration of R6400v2 be wrong? 

Thank you.