Sorry, I am unable to understand the whole thing, if could attach some screenshots to illustrate, that would help.
In the meantime - As I understand, snaps were deleted? So, could you check if "Snapshot autodelete" is enabled on that volume? Might be the case where threshold has been reached and snaps deleted according to the settings. While this is investigated, you could disable "autodelete" setting to prevent snaps from being deleted.
Snapshots are deleted immediately after Snap Center backup is run
https://kb.netapp.com/Advice_and_Troubleshooting/Data_Protection_and_Security/SnapCenter/Snapshots_are_deleted_immediately_after_SnapCenter_backup_is_run
How to use Snapshot Autodelete
https://kb.netapp.com/Advice_and_Troubleshooting/Data_Storage_Software/ONTAP_OS/How_to_use_Snapshot_Autodelete