Backups can contain incompatible config options, thus we only support restoring to the same or newer versions. Compatibility the other way will always be preserved, i.e. you can always restore on a node newer than the one you made the backup on.
Update your nodes to the latest version and try the restore again.
If you really need this, and know what you're doing, go into the template's config /etc/pve/qemu-server/<vmid>.conf
and replace the line starting with boot: order=xxx
with boot: acdn
.