Although I am not able to reproduce it, this obsolete snapshot that "snapper list" does not show must have been created by incorrect system configuration or rather a bug in snapper. However, since I am not able to reproduce I agree this ticket should be closed. I did ask for advice how to delete the obsolete unreachable for snapper snapshot but no reply was provided. For the record, (with some googling) I was able to find the right command that deleted the snapshot successfully, without mounting it: btrfs subvol delete /.snapshots/24/snapshot/ Regards, Atanas