If your Plesk server is behind NAT, you can match private IP addresses on the server to the corresponding public IP addresses via the Plesk...
Please check content of file /root/.autoinstallerrc
Just go to Tools & Settings > PHP Settings > Your PHP version and make sure that module mysqlnd is enabled there.
Perhaps IPv6 is not working on your server since IPv6 kernel module is not loaded and not available at all. Check it with:#modinfo ipv6
If you mean customization of /usr/local/psa/var/modules/wp-toolkit/maintenance/template.phtml template - it will not be overwritten by WPT update.
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