[opensuse-gnome] Web Authentication Redirect just an empty window?

For a couple of weeks now my Web Authentication Redirect windows, that used to work just fine, only come up as an empty window (see attached), even after zypper dup-ing my Tumbleweed system or rebooting it. Using a regular browser (Firefox, Chrome,...) always works and brings me to the respective login page. Any ideas what might be going on or where I should start digging (logs,...)? Gerald