Hi,
To fix it, you can try adding the code below in your child theme’s functions.php file.
// =============================================================================
// Assign sidebar to custom post archives
// =============================================================================
add_filter( 'ups_sidebar', 'assign_post_sidebar' );
function assign_post_sidebar($sidebar){
if (is_singular('post')) {
return 'ups-sidebar-my-sidebar';
}
return $sidebar;
}
// =============================================================================
Don’t forget to replace ups-sidebar-my-sidebar with the actual ID of your custom sidebar as shown below:

Hope that helps