У меня на 3.0.2 выдает аналогичную ошибку при сохранении, даже если просто зайти в карточку товара и нажать сохранить ничего не меняя, визуально на форме ошибок не выводит, в логах такое:
2020-02-27 16:09:32 - PHP Notice: Undefined index: article_review_id in /var/www/html/storage/modification/admin/model/catalog/product.php on line 172
2020-02-27 16:09:32 - PHP Notice: Undefined index: article_parent_id in /var/www/html/storage/modification/admin/model/catalog/product.php on line 175
2020-02-27 16:09:41 - PHP Notice: Undefined index: article_review_id in /var/www/html/storage/modification/admin/model/catalog/product.php on line 172
2020-02-27 16:09:41 - PHP Notice: Undefined index: article_parent_id in /var/www/html/storage/modification/admin/model/catalog/product.php on line 175
2020-02-27 16:09:48 - PHP Notice: Undefined index: article_review_id in /var/www/html/storage/modification/admin/model/catalog/product.php on line 172
2020-02-27 16:09:48 - PHP Notice: Undefined index: article_parent_id in /var/www/html/storage/modification/admin/model/catalog/product.php on line 175
2020-02-27 16:09:55 - PHP Notice: Undefined index: article_review_id in /var/www/html/storage/modification/admin/model/catalog/product.php on line 172
2020-02-27 16:09:55 - PHP Notice: Undefined index: article_parent_id in /var/www/html/storage/modification/admin/model/catalog/product.php on line 175
2020-02-27 16:10:02 - PHP Notice: Undefined index: article_review_id in /var/www/html/storage/modification/admin/model/catalog/product.php on line 172
2020-02-27 16:10:02 - PHP Notice: Undefined index: article_parent_id in /var/www/html/storage/modification/admin/model/catalog/product.php on line 175
Вот здесь, наверное, надо проверять в принципе существование if (isset($data['article_review_id'])), т.к. в массиве $data его в определенных моментах нет
if ($data['article_review_id']) {
$this->db->query("INSERT INTO " . DB_PREFIX . "xl_article_to_product_review SET article_id = '" . (int)$data['article_review_id'] . "', product_id='" . (int)$product_id . "'");
}
if ($data['article_parent_id']) {
$this->db->query("INSERT INTO " . DB_PREFIX . "xl_article_to_product SET article_id = '" . (int)$data['article_parent_id'] . "', product_id='" . (int)$product_id . "'");