The delta download of master data from IS-U into BW can fail if the relevant change pointers are not set active in transaction TBDA2. The relevant change pointers are shown in table ROOSGEN. To activate all change pointers, you can run program RBDCPMIG_ALL_WITHOUT_MIG_FLAG in test mode and after that without test mode. To do so you can use transaction code SE38 and run the program with entry of RS* This procedure has no disadvantages as of my point of view. But thereafter you can load master data from IS-U into BW in delata mode.
Blog about different topics, some of them SAP BW, SAP ABAP and SAP IS-U
Blog über verschiedene Themen, u.a. SAP ABAP und SAP BW und SAP IS-U