[Bitrix\Main\DB\SqlQueryException] 
Mysql query error: (2006) MySQL server has gone away (400)
SELECT 
	`seo_sitemap_iblock`.`SITEMAP_ID` AS `SITEMAP_ID`,
	`seo_sitemap_iblock_sitemap`.`SITE_ID` AS `SITE_ID`,
	`seo_sitemap_iblock_sitemap`.`SETTINGS` AS `SITEMAP_SETTINGS`,
	`seo_sitemap_iblock_iblock`.`CODE` AS `IBLOCK_CODE`,
	`seo_sitemap_iblock_iblock`.`XML_ID` AS `IBLOCK_XML_ID`,
	`seo_sitemap_iblock_iblock`.`DETAIL_PAGE_URL` AS `DETAIL_PAGE_URL`,
	`seo_sitemap_iblock_iblock`.`SECTION_PAGE_URL` AS `SECTION_PAGE_URL`
FROM `b_seo_sitemap_iblock` `seo_sitemap_iblock` 
LEFT JOIN `b_seo_sitemap` `seo_sitemap_iblock_sitemap` ON `seo_sitemap_iblock`.`SITEMAP_ID` = `seo_sitemap_iblock_sitemap`.`ID`
LEFT JOIN `b_iblock` `seo_sitemap_iblock_iblock` ON `seo_sitemap_iblock`.`IBLOCK_ID` = `seo_sitemap_iblock_iblock`.`ID`
WHERE `seo_sitemap_iblock`.`IBLOCK_ID` = 42
/home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php:137
#0: Bitrix\Main\DB\MysqliConnection->queryInternal(string, array, NULL)
	/home/bitrix/www/bitrix/modules/main/lib/db/connection.php:330
#1: Bitrix\Main\DB\Connection->query(string)
	/home/bitrix/www/bitrix/modules/main/lib/entity/query.php:3038
#2: Bitrix\Main\Entity\Query->query(string)
	/home/bitrix/www/bitrix/modules/main/lib/entity/query.php:797
#3: Bitrix\Main\Entity\Query->exec()
	/home/bitrix/www/bitrix/modules/main/lib/entity/datamanager.php:290
#4: Bitrix\Main\Entity\DataManager::getList(array)
	/home/bitrix/www/bitrix/modules/seo/lib/sitemapiblock.php:102
#5: Bitrix\Seo\SitemapIblockTable::getByIblock(array, string)
	/home/bitrix/www/bitrix/modules/seo/lib/sitemapiblock.php:283
#6: Bitrix\Seo\SitemapIblock::__callStatic(string, array)
	/home/bitrix/www/bitrix/modules/main/classes/general/module.php:490
#7: ExecuteModuleEventEx(array, array)
	/home/bitrix/www/bitrix/modules/iblock/classes/general/iblocksection.php:1935
#8: CAllIBlockSection->CheckFields(array, integer)
	/home/bitrix/www/bitrix/modules/iblock/classes/general/iblocksection.php:1097
#9: CAllIBlockSection->Update(integer, array)
	/home/bitrix/www/bitrix/php_interface/init.php:73
#10: MyOnBeforePrologHandler()
	/home/bitrix/www/bitrix/modules/main/classes/general/module.php:475
#11: ExecuteModuleEventEx(array)
	/home/bitrix/www/bitrix/modules/main/include.php:568
#12: require_once(string)
	/home/bitrix/www/bitrix/modules/main/include/prolog_before.php:14
#13: require_once(string)
	/home/bitrix/www/bitrix/modules/main/include/prolog.php:10
#14: require_once(string)
	/home/bitrix/www/bitrix/header.php:1
#15: require(string)
	/home/bitrix/www/catalog/index.php:1
#16: include_once(string)
	/home/bitrix/www/bitrix/modules/main/include/urlrewrite.php:159
#17: include_once(string)
	/home/bitrix/www/bitrix/urlrewrite.php:2

Fatal error: Uncaught Bitrix\Main\DB\SqlQueryException: Mysql query error: (2006) MySQL server has gone away in /home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php:137 Stack trace: #0 /home/bitrix/www/bitrix/modules/main/lib/db/mysqlcommonconnection.php(132): Bitrix\Main\DB\MysqliConnection->queryInternal('SELECT * FROM `...') #1 /home/bitrix/www/bitrix/modules/main/lib/db/connection.php(716): Bitrix\Main\DB\MysqlCommonConnection->getTableFields('b_sec_session') #2 /home/bitrix/www/bitrix/modules/main/lib/db/sqlhelper.php(387): Bitrix\Main\DB\Connection->getTableField('b_sec_session', 'SESSION_ID') #3 /home/bitrix/www/bitrix/modules/main/lib/entity/datamanager.php(974): Bitrix\Main\DB\SqlHelper->prepareAssignment('b_sec_session', 'SESSION_ID', 'P4t00nyEBzHnXI2...') #4 /home/bitrix/www/bitrix/modules/security/classes/general/session_db.php(92): Bitrix\Main\Entity\DataManager::delete(Array) #5 [internal function]: CSecuritySessionDB::write('P4t00nyEBzHnXI2...', 'SESS_AUTH|a:1:{...') #6 [internal function]: sess in /home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php on line 137