Catch Theme “Mustang”, Version 4.0.1: Customizer & THEME OPTIONS failure

Our Wordpress Catch Theme "Mustang", Version 4.0.1 is not working properly. It is a brandnew wordpress 6.7.2 installation without any plugins, exept the "Classic Editor" plugin. You can find the website of our musical band at https://www.pophookers.de CUSTOMIZER: - We've added "Additional CSS" in the "Customizer". The additional CSS is active in the preview of the website but not on the live website. The same with "Theme Options/Header Options" in the Customizer: We can disable the header search here. It seems like that is is saved but not published. - From time to time all settings of the Cusomizer are gone and we have to do it all from the beginning, even if we're not logged in. THEME OPTIONS: It isn't possibe to save here anything, after we press the save button we'll get an error message. We're familiar with this Theme and use it at two different websites, there it works properly. Can you please help in this case? Regards, / Andreas