I ran into this issue and resolved it by making sure the id value was not removed from the sidebar makrup:
For example, this one does not work
$args = array(
‘name’ => __(‘Right Sidebar’, ‘theme_text_domain’),
‘id’ => ‘right-sidebar’,
‘description’ => ”,
‘class’ => ”,
‘before_widget’ => null,
‘after_widget’ => null,
‘before_title’ => ‘<h2 class=”widgettitle title-green widget %2$s”>’,
‘after_title’ => ‘</h2>’);
while this one does
$args = array(
‘name’ => __( ‘Right Sidebar’, ‘theme_text_domain’ ),
‘id’ => ‘right-sidebar’,
‘description’ => ”,
‘class’ => ”,
‘before_widget’ => ‘<div id=”%1$s” class=”widget %2$s”>’,
‘after_widget’ => ‘</div>’,
‘before_title’ => ‘<h2 class=”widgettitle title-green”>’,
‘after_title’ => ‘</h2>’ );
Make sure “id=”%1$s” is present inside the markup under before_widget