Hardware Version: Archer VR2800v v1

Firmware Version: 1.2.0 0.9.1 v006d.0 Build 180410 Rel.61139n

Hello,

I tried to set up the dynamic dns on my router with the input mask for spdns and from time to time I got the error message "502 Bad Gateway". So I used the custom setting with the update url "https://update.spdyn.de/nic/update?hostname=<domain>&myip=<ip>&user=<user>&pass=<passwd>" which is working fine for the most part. But occasionally - maybe once a week - the update doesn't work and this message is displayed:

Finish with ddns server reply:
HTTP/1.1 401 Unauthorized
Server: openresty
Date: Wed, 07 Nov 2018 02:00:54 GMT
Content-Type: text/html; charset=UTF-8
Connection: close
Set-Cookie: PHPSESSID=6l9igbsd3q985rjtmu4dgkj7qt; expires=Wed, 07-Nov-2018 03:00:54 GMT; Max-Age=3600; path=/; secure; HttpOnly
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate
Pragma: no-cache
Set-Cookie: PHPSESSID=deleted; expires=Thu, 01-Jan-1970 00:00:01 GMT; Max-Age=0; path=/
badauth

This only happens if the router reconnects automatically at 3 am. When I force an update with "Log out" and "Log in" under dynamic dns settings it works just fine. There is no log entry at my ddns provider.
Is there any solution or workaround?