A client’s website was continuously getting PHP Notices regarding PHP session clean up issues. The solution turned out to be more complicated than initially thought, sessions need to be moved into RAM.
A quick solution for this is to disable PHP from displaying Notices
error_reporting = E_ALL & ~E_DEPRECATED & ~E_NOTICE & ~E_WARNING
Put the above in your php.ini at /etc/php.ini. The above will disable deprecation messages, notices and warning messages.