Hello, @Oliver Theiß,
It looks like the issue is not coming from our theme. Would you please first check your issue by activating the WordPress default theme like (Twenty Twenty Two) you will find the same issue which makes it clear that the issue is not because of our theme.
Once the plugin works fine with the default theme it will work fine with our theme too. You can also check the plugin support forums or contact the plugin author for further assistance.
Regards 8Themes Team.