Адаптация 2.3.6 к php 8

Пытаюсь адаптировать свои форумы к php8. Дошел до авторизации, после ввода логин-пароля получаем 

[27-Jul-2021 18:18:14 UTC] PHP Fatal error:  Uncaught Error: Call to a member function simple_exec_query() on null in /home/vors01717457/public_html/ips_kernel/class_converge.php:188
Stack trace:
#0 /home/vors01717457/public_html/sources/loginauth/login_core.php(148): class_converge->converge_load_member()
#1 /home/vors01717457/public_html/sources/loginauth/internal/auth.php(80): login_core->auth_local()
#2 /home/vors01717457/public_html/sources/handlers/han_login.php(192): login_method->authenticate()
#3 /home/vors01717457/public_html/sources/action_public/login.php(576): han_login->login_authenticate()
#4 /home/vors01717457/public_html/sources/action_public/login.php(81): login->do_log_in()
#5 /home/vors01717457/public_html/index.php(580): login->auto_run()
#6 {main}
  thrown in /home/vors01717457/public_html/ips_kernel/class_converge.php on line 188

Там у нас функция

public function converge_load_member($email)
	{
		if ( ! $email )
		{
			$this->member = array();
		}
		else
		{
		  	$this->member = $this->converge_db->simple_exec_query( array( 'select' => '*', 'from' => 'members_converge', 'where' => "converge_email='$email'" ) );
		}
	}

Где-то в simple_exec_query ошибка, но не пойму где.

function simple_exec_query( $a )
    {
    	return $this->build_and_exec_query( $a );
    }

function build_and_exec_query( $a )
    {
    	$this->build_query( $a );

    	$ci = $this->exec_query();
    	
    	if ( isset($a['select']) AND $a['select'] )
    	{
    		return $this->fetch_row( $ci );
    	}
    }

Благодарю за любую помощь.