How to identify the balance mismatch in Customer reconciliation GL and Age analysis report?

Dear Expert,

Our business is facing balance mismatch between GL account and Customer age analysis. They do the reconciliation between customer reconciliation GL account with custom age analysis report. But every month we found some differences on that 2 balances. We debug the custom report and checked the table (BSID, BSAD, KNKK) one by one which is used on that report. But we couldn't identify the exact reason which causes the balance mismatch.

Could you please assist us with your ideas to resolve this issue soon?

Regards,

Shreekum