500 error only in privacy mode (chrome)

We have a NSS 5.2.3 (Docker Container) running in our kubernetes behind traefik with a certificate by lets encrypt.

We are testing the chess app (https://pheyvaer.github.io/solid-chess/) and it's working for a normal chrome session.

But in privacy mode or in Chromium, we will got the following error for the GET request https://localhost/inbox/ with status 500:
request to https://localhost/.well-known/openid-configuration failed, reason: unable to verify the first certificate

We tested also against inrupt.net and there is no problem.

We compared the requests and found out, that the cookie nssidp.sid is missing.

We tried some startup parameters, but with no effect.

We think that is not a specific NSS issue more like general purpose for proxying or security measures.

Empieza reproduciendo la solicitud GET a https://localhost/inbox/ en el modo de privacidad de Chrome o en Chromium y compárala con una sesión normal. Rastrea el fallo de verificación del certificado de /.well-known/openid-configuration y la cookie nssidp.sid ausente a través de NSS, Docker, Kubernetes y Traefik; se considera terminado cuando la solicitud tiene éxito sin el error 500.