problem not solved, WPX have said this:
Hi Vlad,
After investigating, I can confirm that the issue is due to the Multiple Pages Generator by Themeisle plugin.
You can see the error in the error log as well:
PHP Fatal error: Allowed memory size of 536870912 bytes exhausted (tried to allocate 131072 bytes) in /home/dritcoux/public_html/wp-content/plugins/multiple-pages-generator-by-porthas/helpers/Helper.php on line 636
Despite how it looks, this is not exactly a memory issue, as you have plenty of it to accommodate the query.
The issue would be with how the queries are generated, in this case, most likely, flooding meta- and term-data, which exhausts the website memory in a way independent of the set PHP memory limit, though with this plugin, this may be slightly different.
As far as I am aware, this could most likely be addressed by editing the core WordPress files, but that could break your website, hence why it is not included in our provided support services.
I would advise you to either remove the plugin or contact their support services so they can take a look at the matter and provide a solution.