You will need to submit a Missing Cashback request for every order that is missing.
Here's where you can do it:
1) On the mobile app, click on the user icon
2) Search for "Report Missing Cashback" and select "ShopBack In-Store Transaction"
3) Submit your Missing Cashback request
The investigation takes 7-14 days to be completed
IMPORTANT: Missing Cashback submissions must be within 30 days from the purchase date. Any submissions past the specified time are invalid and will not be investigated by the network.