Nextcloud desktop client disconnect when starting

Nextcloud version (eg, 18.0.2): 17.0.2
Operating system and version (eg, Ubuntu 20.04): Alpine Linux 3.8.0
Apache or nginx version (eg, Apache 2.4.25): nginx 1.18.0
PHP version (eg, 7.1): 7.3.17

The issue you are facing:
My issue is related to Nextcloud desktop client version 2.6.4-1 installed on Arch LInux with Xfce4 desktop.
The setup of the client is finished w/o errors and everything works as expected.
However when I start my desktop PC the client is disconnected from server.
The client then opens a browser window automatically in order to authenticate against the server.

This is annoying because I would expect that the authentication is stored after successful setup and must not be always repeated after each desktop start.

I configured the client to write a logfile and this shows following entries:

alse,"productname":"Nextcloud","version":"17.0.2.1","versionstring":"17.0.2"})   QNetworkReply::NoError  Reply:  QNetworkReplyHttpImpl(0x55a37ca24a40)
[OCC::ConnectionValidator::slotStatusFound      ** Application: ownCloud found:  QUrl("https://<nextcloud URL>")  with version  "17.0.2" ( "17.0.2.
1" )
[OCC::ConnectionValidator::setAndCheckServerVersion     QUrl("https://meiklaud.biszumbitterenen.de") has server version "17.0.2.1"
[OCC::AccountState::slotConnectionValidatorResult       AccountState connection status change:  OCC::ConnectionValidator::Undefined -> OCC::ConnectionValidator:
:CredentialsNotReady

Is this the first time you’ve seen this error? (Y/N): Y

Steps to replicate it:

  1. Start Nextcloud client

My simple question is:
Why is Nextcloud desktop client not storing authentication data with Xfce4?

THX