StyleDefinery replied
Thanks for the quick answer. Apparently it was because the theme was not activated. After the activation everything works fine.
But I still get the message that there is an update of WPBakery, but when I try to download it I get the following error message:
Update failed: To receive automatic updates license activation is required. Please visit Settings to activate your WPBakery Page Builder. Got WPBakery Page Builder in theme?
Do I need to buy the WPBakery-License to get the updates?