Nintendo Switch Error Code 2618-0516

Hi everyone,
I always get the error code 2618-0516 when I play any game. My internet connection is up and I also get into the game, but when I start a match, I always get this error message after 10 seconds. It’s been going on for a whole day now …
Does anyone have any idea what I can do about it?
Thanks in advance

Seems to be an NAT related network problem.

Searching on the web you will find some results, e.g.