Query on Obsolete Line Item in APO

Hello,

I want to understand what is the reason of Obsolete line item in APO which we get when we run //SDRQCR21 report in APO. When I dig in I found that there was double allocation in AC42 for the order - Main line item and sub line item both was consuming the qty in AC42. What can be the reason there is double consumption in AC42. I tried to trace the issue and look for the pattern, but there is no such pattern and happening randomly.

Any help will great to troubleshot the issue.

Regards

Andy