Transaction group disappears after 1 week when trying to mass approve asset

Summary:

Hi Team, we would want to utilize the mass approve functionality for asset additions. We created one transaction group and created 5 to 6 assets and selected approval type as 'Mass' and Transaction Group as 'Additions' and then the approver got one notification for all the 6 assets which was sent for approval which is working as expected.

After one week, when we are creating a new asset and selecting the Approval type as 'Mass' the Transaction group shows no values it seems to be blank. Not sure why the transaction group gets disappeared after a few days, What is the best practice to define the same. Please let me know