Fatal error: Allowed memory size… when access to AllPosts

Ciao, I kindly ask your support for solving this issue:
when I access AllPosts from admin panel, only after this action and moreover the site OrlandoFurioso is perfectly working, I get the following error:
Fatal error: Allowed memory size of 268435456 bytes exhausted (tried to allocate 72 bytes) in /home/xxxxxxxxxx/public_html/wp-includes/wp-db.php on line 1941
I already tried:
– increase new memory limit editing wp-config.php
– in php.in the memory_limit = 1024M
– ask the hosting provider to increase the memory limit
– deactivate and then activate again both the plugins and the template
…but the problem still persist!

Any suggestion on how to solve it?

Thank you in advance! ??