Error in MODX xpdo.class.php?

Question

MODX

Hello, I have encountered the following error.
1. When I go to a certain page of the site, I get the following error
Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 262144 bytes) in .../core/xpdo/xpdo.class.php on line 591
2. The resource itself page from the admin is not deleted. Nothing happens when 'Delete Section' is selected
3. The following is written in the log
(ERROR @ Unknown0) PHP warning: Unknown: Failed to write session data using user defined save handler. (session.save_path: /var/lib/php/sessions)
(ERROR @ /home/u630315/triumf-kolomna.ru/html/core/xpdo/om/xpdoobject.class.php : 240) Error HY000 executing statement:
Array
(
[0] => HY000
[1] => 2014
[2] => Cannot execute queries while other unbuffered queries are active. Consider using PDOStatement::fetchAll(). Alternatively, if your code is only ever going to run against mysql, you may enable query buffering by setting the PDO::MYSQL_ATTR_USE_BUFFERED_QUERY attribute.
MODX version 2.6.5
Thanks in advance.