Hello @Shrutii
The DB Clean-up workflow deletes the data from the list where you have the expiry date.
If there is no expiry date, then a recent instance upgrade could be one of the reasons for this. This is a known issue: the lists are purged when Adobe upgrades the instance due to some bug.
Unfortunately, you can't do anything now.
One of the options is to restore the DB backup but doing this, you will lose any changes that is made to platform after the upgrade.