Turns out it was multiple things. Automatic import of pools was disabled in ubuntu package. Can be overridden with kernel module setting but that isn't an option since it then breaks zroot import for pivot root.
Solution was to copy data from zboot to /boot on zroot, destroy that pool, and update initramfs as well as the grub. Now boot is being done normally from zroot (both /boot and pivot root) and zpool.cache doesn't get erased during that process, so storage pool gets imported normally.
social.tomica.me is one server in the network