Hello,
To debug the material initial load, you can follow the below steps:
- Deregister queue R3AI_MATERIAL in txn: SMQR
- R3AC1, MATERIAL, give the correct source and destination
- /h and then execute
- Settings-->Debugging (Background Task: tick Do Not Process) Hope I remember it correctly 
- F8 or execute.
- Check txn: SMQ1. Queue like R3AI_MATERIAL should be waiting there.
- Click on debug.
- You can keep the breakpoints at extractor CRS_MATERIAL_EXTRACT and MW module CRS_SEND_TO_SERVER.
- At CRS_SEND_TO_SERVER, check the BAPI structures to know what data has been extracted.
- Then put BP at CRM_FILTER_DOWNLOAD_DATA.
- After execution of above module, confirm that material data still present in BAPI structure.
- Then comes the user exit on R/3 side. There is some module like OPEN_PI* within CRS_SEND_TO_SERVER. You need to go inside this module to confirm no user exit exists and even if they exist, they are not removing the material data.
- So even after this module data exists in BAPI structure then materials are atleast reaching CRM.
- Next point you can check is CRM I/B. Check SMQ2 for R3AI_MATERIAL and put BP at
COM_MAP_PRODUCT_MAT_TO_BAPIMTCS (use * if this is not the correct mapper name).
- You can also debug this module which has simple performs to map ECC data to CRM data.
You can also refer blogs from Jerry Wang, to know the detailed steps.
Hope this helps!
Best Regards,
Shanthala.