Comment # 6 on bug 1068197 from Atanas Bombov

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