Hi,
I am assuming you have CIF'd the Business partner from ECC as both location & BP. If the BP from Location has been manually removed by someone, only CIF Initial transfer will bring it across. If the Business Partner field was not populated in APO Location Master during Initial Transfer, you might have to check you CIF logs for any messages. I suggest you start with looking at Change Documents for those 6 locations in APO (if they are active).
Regards
AK