Thanks Shubh for your feedback

If somehow your snapshot 2 got deleted then snapshot 3 will start referencing to snapshot 1 for unchanged data. The compute instance will mark snapshot as DELETED and all the unique data of snapshot 2 will transferred to snapshot 3, this make your snapshot 3 bigger in size due to movement of data.

For more information visit this link: https://cloud.google.com/compute/docs/disks/restore-and-delete-snapshots#deleting_snapshot