[Big Sur] Edited system volume, sealed snapshot got deleted

Hi,

So I followed the steps on dortania.github.io to edit my system volume and create a new bootable snapshot.

I had (and have) to disable SIP, including the authenticated-root flag. So far so good.

However, to my surprise, the original, sealed com.apple.os.update-GUID snapshot just disappeared... I have also noticed that if I keep recreating new snapshots, the old ones disappear on reboot. I cannot seem to keep more than one snapshot, any ideas why?

I have noticed the new, non-sealed snapshots are purgeable. However, even though I didn't check before it got deleted, I'm pretty sure the sealed com.apple.os.update-GUID snapshot must have been non-purgeable?!...