Thanks for the help guys,
unfortunately, the process wasn't willing to time out, even with local hosts entries.
So I opened a SR and the guys from GSS were able to help me.
The solution was to trigger the scan and update from the command line. So the appliance is updated now and the Update Tab in in the web frontend works as intended now.
1. Log into Appliance with SSH
2. /opt/vmware/bin/vamicli update --check
3. /opt/vmware/bin/vamicli update --install latest --accepteula
Regards
Tim