Hi there,
unfortunately some things in the customizer section do not work after I updated WP for example the “Add + Edit …” Buttons which of course are important for changing the content of the sections. I already tried to downgrade to 4.8. but nothing changed…
Please help 
Hello there,
I hope you are doing well today.
This could be a PHP issue so please contact your hosting provider and have them check to ensure that you are using PHP version 5.6 or greater.
Best Regards,
Support