Voucher Posting Not Creating Correct Statistics Code or Statistic Amount Correctly

Hello,

When journal generating the AP voucher journals, our business users came across where some vouchers did not contain the statistics code or statistic amount that were entered on the AP voucher.  After analysis of these vouchers, the data showed the statistic code and amount were entered in the PS_DISTRIB_LINE but were not inserted into the PS_VCHR_ACCTG_LINE.  The voucher posting process was successful and there were some that were created correctly and some that were not but they were different process instances.  Has anyone ran into this issue?  What can cause the AP_PSTVCHR process to not copy over the statistics code