[Bitrix\Main\DB\SqlQueryException] 
Mysql query error: (2006) MySQL server has gone away (400)
SELECT 
	`main_user_field`.`ID` AS `ID`,
	`main_user_field`.`ENTITY_ID` AS `ENTITY_ID`,
	`main_user_field`.`FIELD_NAME` AS `FIELD_NAME`,
	`main_user_field`.`USER_TYPE_ID` AS `USER_TYPE_ID`,
	`main_user_field`.`XML_ID` AS `XML_ID`,
	`main_user_field`.`SORT` AS `SORT`,
	`main_user_field`.`MULTIPLE` AS `MULTIPLE`
FROM `b_user_field` `main_user_field` 

WHERE `main_user_field`.`ENTITY_ID` = 'PRODUCT'
ORDER BY `SORT` ASC, `ID` ASC
/var/www/html/bitrix/modules/main/lib/db/mysqliconnection.php:146
#0: Bitrix\Main\DB\MysqliConnection->queryInternal
	/var/www/html/bitrix/modules/main/lib/db/connection.php:327
#1: Bitrix\Main\DB\Connection->query
	/var/www/html/bitrix/modules/main/lib/orm/query/query.php:3558
#2: Bitrix\Main\ORM\Query\Query->query
	/var/www/html/bitrix/modules/main/lib/orm/query/query.php:952
#3: Bitrix\Main\ORM\Query\Query->exec
	/var/www/html/bitrix/modules/main/lib/orm/data/datamanager.php:513
#4: Bitrix\Main\ORM\Data\DataManager::getList
	/var/www/html/bitrix/modules/catalog/general/querybuilder.php:814
#5: CProductQueryBuilder::getProductUserFields
	/var/www/html/bitrix/modules/catalog/general/querybuilder.php:617
#6: CProductQueryBuilder::initEntityFields
	/var/www/html/bitrix/modules/catalog/general/querybuilder.php:103
#7: CProductQueryBuilder::isValidField
	/var/www/html/bitrix/modules/iblock/classes/general/iblockelement.php:2687
#8: CAllIBlockElement->PrepareGetList
	/var/www/html/bitrix/modules/iblock/classes/mysql/iblockelement.php:326
#9: CIBlockElement->prepareSql
	/var/www/html/bitrix/modules/iblock/classes/mysql/iblockelement.php:666
#10: CIBlockElement::GetList
	/var/www/html/bitrix/modules/primelab.urltosef/include.php:629
#11: CPrimelabUrlToSEF::OnPageStart
	/var/www/html/bitrix/modules/main/classes/general/module.php:480
#12: ExecuteModuleEventEx
	/var/www/html/bitrix/modules/main/include.php:159
#13: require_once(string)
	/var/www/html/bitrix/modules/main/include/prolog_before.php:14
#14: require_once(string)
	/var/www/html/bitrix/modules/main/include/prolog.php:10
#15: require_once(string)
	/var/www/html/bitrix/header.php:1
#16: require(string)
	/var/www/html/catalog/index.php:2
#17: include_once(string)
	/var/www/html/bitrix/modules/main/include/urlrewrite.php:184
#18: include_once(string)
	/var/www/html/bitrix/urlrewrite.php:2
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