As it turns out gdisk/sgdisk have since the dawn of time written labels byte-swapped on s390x.
We'll continue to help in the upstream discussion and once a solution is available consider backporting (or not as it might wreak more havoc than not).
Affected are all releases since Xenial and also nonUbuntu like Fedora34 where I confirmed the same.
As it turns out gdisk/sgdisk have since the dawn of time written labels byte-swapped on s390x.
We'll continue to help in the upstream discussion and once a solution is available consider backporting (or not as it might wreak more havoc than not).
Affected are all releases since Xenial and also nonUbuntu like Fedora34 where I confirmed the same.