Сделано в sistemgroup.ru 
[Bitrix\Main\DB\SqlQueryException] 
Mysql query error: (2006) MySQL server has gone away (400)
SELECT GET_LOCK('47f668c2d1c40a6c7595666c35e19ce9d876a3a5b5ef2e29184eba200ebedb0a', 0) as L
/home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php:149
#0: Bitrix\Main\DB\MysqliConnection->queryInternal
	/home/bitrix/www/bitrix/modules/main/lib/db/connection.php:331
#1: Bitrix\Main\DB\Connection->query
	/home/bitrix/www/bitrix/modules/main/lib/db/mysqlcommonconnection.php:299
#2: Bitrix\Main\DB\MysqlCommonConnection->lock
	/home/bitrix/www/bitrix/modules/main/classes/mysql/user_counter.php:681
#3: CUserCounterPage::checkSendCounter
	/home/bitrix/www/bitrix/modules/main/classes/general/main.php:3739
#4: CAllMain::RunFinalActionsInternal
	/home/bitrix/www/bitrix/modules/main/lib/application.php:368
#5: Bitrix\Main\Application->terminate
	/home/bitrix/www/bitrix/modules/main/lib/application.php:329
#6: Bitrix\Main\Application->end
	/home/bitrix/www/bitrix/modules/main/classes/general/main.php:3715
#7: CAllMain::FinalActions
	/home/bitrix/www/bitrix/modules/main/include/epilog_after.php:61
#8: require(string)
	/home/bitrix/www/bitrix/modules/main/include/epilog.php:3
#9: require_once(string)
	/home/bitrix/www/bitrix/footer.php:4
#10: require(string)
	/home/bitrix/www/catalog/index.php:818
#11: include_once(string)
	/home/bitrix/www/bitrix/modules/main/include/urlrewrite.php:184
#12: 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:149 Stack trace: #0 /home/bitrix/www/bitrix/modules/main/lib/db/mysqlcommonconnection.php(89): Bitrix\Main\DB\MysqliConnection->queryInternal() #1 /home/bitrix/www/bitrix/modules/main/lib/db/connection.php(819): Bitrix\Main\DB\MysqlCommonConnection->getTableFields() #2 /home/bitrix/www/bitrix/modules/main/lib/db/sqlhelper.php(436): Bitrix\Main\DB\Connection->getTableField() #3 /home/bitrix/www/bitrix/modules/main/lib/orm/data/datamanager.php(1674): Bitrix\Main\DB\SqlHelper->prepareAssignment() #4 /home/bitrix/www/bitrix/modules/main/lib/session/handlers/databasesessionhandler.php(60): Bitrix\Main\ORM\Data\DataManager::delete() #5 /home/bitrix/www/bitrix/modules/main/lib/session/handlers/databasesessionhandler.php(38): Bitrix\Main\Session\Handlers\DatabaseSessionHandler->processDestroy() #6 /home/bitrix/www/bitrix/modules/main/lib/session/handlers/abstractsessionhandler.php(88): Bitrix\Main\Session\Handlers\DatabaseSessionHandler->processWrite() #7 [internal function]: Bitrix\Main\Session\Handlers\AbstractSessionHandler->write() #8 [internal function]: session_write_close() #9 {main} thrown in /home/bitrix/www/bitrix/modules/main/lib/db/mysqliconnection.php on line 149