In ISPConfig Panel System | Server Config | Web I edited PHP settings. They were PHP 5.6 still after upgrading from Debian 9 to Debian 10. I changed the PHP settings by copying from a host that has ISPConfig 3.1.15 installed on Debian 10. I copy pasted all except PHP-FPM pool directory, which I let stay. After saving I tested with htf-common-issues.php and it still showed Code: [INFO] php-cgi (used for cgi php in default vhost!) is version 5.6.40-0+deb8u2 Wondering why I checked what I wrote, and all the values in PHP settings were empty. I tried copy pasting them again, but got error when saving about website settings. Checking those I saw they were also empty. At this point I went Monitor | Data Log History and undid that change. Now looks like all is back but I dare not try this again until understand what happened and how this PHP settings change should be done.