There is a very rare issue where the veth device isn't properly removed when the PHP version is changed during a period of high load. I'm 99% sure a reboot will fix it.
The other possibility is that something has been customised in the php-fpm config or that Ubuntu has been changed to a new release (ie. 22.04 -> 24.04) without updating the ecp-php* packages.
If you can't fix it, please send a support ticket.
