The sidebar bullets were broken by a Divi update that changed the class name used on individual post pages. Archive and search pages with sidebars were not affected. To correct this, add the below CSS to your child theme or in Divi > Theme Options > General > Custom CSS:

/* Fix Sidebar Bullets on Single Posts */

div#recent-posts-2.et_pb_widget.widget_recent_entries.et_pb_widget li:before, div#archives-2.et_pb_widget.widget_archive.et_pb_widget li:before, div#categories-2.et_pb_widget.widget_categories.et_pb_widget li:before {
    content: ' ';
    position: absolute;
    background: #43BFB4;
    width: 13px;
    height: 13px;
    border-radius: 50%;
    margin: 7px 0 0 0;

Please ensure you update the bullet color to match your site and clear all caches once your changes are saved.