Release status is not appearing for Sales orders after Running the Backlog plan?

Summary:

After completing data collection, the Backlog Plan was run for the first time using the ESS job “Start Backlog Planning.”

We observed that for some sales order lines the Release Status is blank, whereas for other sales orders with the same Item, Organization, Customer, and Ship-to Site combination, the Release Status shows as “Release”

For the order lines where the Release Status is blank, the “Mark for Release” action is not able to perform, and we are unable to release the planning recommendations.

What could be the possible reasons why the Release Status would remain blank for certain sales order lines under the same setup and what checks or configurations we should review?