Сделано в sistemgroup.ru
[Bitrix\Main\DB\SqlQueryException] 
Mysql query error: (2006) MySQL server has gone away (400)
SELECT * FROM `b_user_session` LIMIT 0
/home/bitrix/www/bitrix/modules/main/lib/db/mysqlcommonconnection.php:415
#0: Bitrix\Main\DB\MysqlCommonConnection->createQueryException
	/home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php:149
#1: Bitrix\Main\DB\MysqliConnection->queryInternal
	/home/bitrix/www/bitrix/modules/main/lib/db/mysqlcommonconnection.php:90
#2: Bitrix\Main\DB\MysqlCommonConnection->getTableFields
	/home/bitrix/www/bitrix/modules/main/lib/db/connection.php:821
#3: Bitrix\Main\DB\Connection->getTableField
	/home/bitrix/www/bitrix/modules/main/lib/db/sqlhelper.php:435
#4: Bitrix\Main\DB\SqlHelper->prepareAssignment
	/home/bitrix/www/bitrix/modules/main/lib/orm/data/datamanager.php:1660
#5: Bitrix\Main\ORM\Data\DataManager::delete
	/home/bitrix/www/bitrix/modules/main/lib/session/handlers/databasesessionhandler.php:60
#6: Bitrix\Main\Session\Handlers\DatabaseSessionHandler->processDestroy
	/home/bitrix/www/bitrix/modules/main/lib/session/handlers/databasesessionhandler.php:38
#7: Bitrix\Main\Session\Handlers\DatabaseSessionHandler->processWrite
	/home/bitrix/www/bitrix/modules/main/lib/session/handlers/abstractsessionhandler.php:87
#8: Bitrix\Main\Session\Handlers\AbstractSessionHandler->write
	
#9: session_write_close
	/home/bitrix/www/bitrix/modules/main/lib/application.php:371
#10: Bitrix\Main\Application->terminate
	/home/bitrix/www/bitrix/modules/main/lib/application.php:329
#11: Bitrix\Main\Application->end
	/home/bitrix/www/bitrix/modules/main/classes/general/main.php:3708
#12: CAllMain::FinalActions
	/home/bitrix/www/bitrix/modules/main/include/epilog_after.php:61
#13: require(string)
	/home/bitrix/www/bitrix/modules/main/include/epilog.php:3
#14: require_once(string)
	/home/bitrix/www/bitrix/footer.php:4
#15: require(string)
	/home/bitrix/www/catalog/index.php:829
#16: include_once(string)
	/home/bitrix/www/bitrix/modules/main/include/urlrewrite.php:128
#17: include_once(string)
	/home/bitrix/www/bitrix/urlrewrite.php:2
----------