Hello, Florian
Thank you for reaching out to us.
In order to further investigate the issue, we kindly request that you provide us with temporary WordPress admin and FTP access.
To provide wp-admin access, you can create a new user account with administrator role via the Dashboard, and provide us with the username and password via the Private Content area.
To provide FTP access, please contact your hosting provider for assistance.
We look forward to hearing from you.
Kind Regards,
8theme team