Undefined index: id in /var/www/html/usmlocal/vendor/magento/module-config/Model/Config/Structure/Element/Iterator.php code example

Example: Exception #0 (Exception): Notice: Undefined index: id in /var/www/html/vendor/magento/module-config/Model/Config/Structure/Element/Iterator.php on line 63

One easy way to debug is: browse and open vendor/magento/module-config/Model/Config/Structure/Element/Iterator.php

change

public function setElements(array $elements, $scope)
    {
        $writer = new \Zend\Log\Writer\Stream(BP . '/var/log/config_debug.log');
        $logger = new \Zend\Log\Logger();
        $logger->addWriter($writer);
        
        $this->_elements = $elements;
        $this->_scope = $scope;
        
        if (count($elements)) {
            $lastElement = end($elements);

            // Log last Element
            $logger->info($lastElement);

            $this->_lastId = $lastElement['id'];
        }
    }