Hazard state of Btrfs snapshots after dup

Yesterday I upgraded my Tumbleweed and all my existing btrfs snapshots up to this moment disappeared into oblivion.
Intrigued I returned the previous copy of Tumbleweed VM, luckily for me it was a KVM guest and tried again.
The second time some snapshots disappeared, some remained - both kinds - important & not important. And I cannot catch the logic of it.
I’ve never experienced such behavior of dup before.
My question is this a new behavior of Tumbleweed dup, and if it is why then is not deterministic and produces the same results?
Or is it some kind of a lurking Btrfs bug?
My Tumbleweed KVM guest is a LUKS Full Disk Encrytped Btrfs, if this matters in this case.