eizellspende
Hi,
The problem comes from the PHP settings on your server side, the setting "Maximum Input Variables' is set a bit low (1000) you can see this settings in Backend > System Information > PHP settings
If you have permission to change this settings in server side, normally change via php.ini file in server, pls increase this value to at least 2000 as above screenshot, it will work fine. In case, you don't have permission, contact your hosting provider for help to change this.
Regards