Bluehost Too Many Connections Error Although There is No Traffic - mysql

Question

We have a Wordpress website in development stage hosted on Bluehost shared hosting. Although there is no traffic, I get this error:
Warning: mysqli_real_connect(): (08004/1040): Too many connections in /wp-includes/class-wpdb.php on line 1775
Too many connections
This happens randomly. And I use global $wpdb for every database queries I make. According to https://wordpress.stackexchange.com/questions/117495/database-connection-close wpdb class automatically closes the connection. So we should have only one or two active connections as the site is not accessible by public.
wp-config.php file content
define('DB_NAME', 'example');
define('DB_USER', 'example');
define('DB_PASSWORD', 'example');
define('DB_HOST', 'localhost');
define( 'DB_CHARSET', 'utf8' );
define( 'DB_COLLATE', '' );
define('AUTH_KEY', 'example');
define('SECURE_AUTH_KEY', 'example');
define('LOGGED_IN_KEY', 'example');
define('NONCE_KEY', 'example');
define('AUTH_SALT', 'example');
define('SECURE_AUTH_SALT', 'example');
define('LOGGED_IN_SALT', 'example');
define('NONCE_SALT', 'example');
$table_prefix = '8zW_';
define('WP_CRON_LOCK_TIMEOUT', 120);
define('AUTOSAVE_INTERVAL', 300);
define('WP_POST_REVISIONS', 5);
define('EMPTY_TRASH_DAYS', 7);
define('WP_AUTO_UPDATE_CORE', true);
define( 'WP_DEBUG', true );
if ( ! defined( 'ABSPATH' ) ) {
define( 'ABSPATH', __DIR__ . '/' );
}
require_once ABSPATH . 'wp-settings.php';