NextcloudPi UI does no longer launch from within the Nextcloud UI after ncp auto-upgraded Nextcloud from v25 to v26.0.3

my NextcloudPi has been running for serveral years and has been auto-upgraded successfully serveral times already.
A few days ago ncp v1.52.1 auto-upgraded my NC instance to version 26.0.3 (unattended upgrade). NC itself is runnig without issues but I can no longer access the NCP web ui.

When clicking to the NCP icon from within the NC ui I get the following output.


Any ideas to resolve this issue would be much appreciated.

UPDATE: If I call NCP directly on port 4443 it launches. So the issue is only related to launching it via the NCP icon from within the Nextcloud UI.