I figured out that the call of "do_action( 'sidebar_admin_setup' );" in siteorigin-panels.php#337 causes an error which breaks the WP theme customizer.
After commenting the line out of the plugin code, the customizer works again.
Another thing I figured out is that the problem can be solved when I delete the templates widgets from the footer.
I'm not sure what the problem is with the sidebar and/or the widgets, but here a code example that you know what I#m talking about.
if ( ! function_exists( 'foobar_widgets_init' ) ):
function foobar_widgets_init() {
register_sidebar( array(
'name' => __( 'Footer (center)', 'foobar' ),
'id' => 'footer-center',
'description' => __( 'Add widgets here to appear in the middle of the footer.', 'foobar' ),
'before_widget' => '<div id="%1$s" class="%2$s">',
'after_widget' => '</div>',
'before_title' => '<h4>',
'after_title' => '</h4>',
) );
register_sidebar( array(
'name' => __( 'Footer (right)', 'foobar' ),
'id' => 'footer-right',
'description' => __( 'Add widgets here to appear on the right of the footer.', 'foobar' ),
'before_widget' => '<div id="%1$s" class="%2$s">',
'after_widget' => '</div>',
'before_title' => '<h4>',
'after_title' => '</h4>',
) );
}
add_action( 'widgets_init', 'foobar_widgets_init' );
endif;
I tested some free templates from the WordPress community. You can reproduce it for example with the theme "i-excel".
If you add a widget to the "Main Widget Area" sidebar, the theme customizer at http://yourdomain.com/wp-admin/customize.php?theme=i-excel will not work anymore.