Mass Upload Problem with BAPI_BILLINGDOC_CREATEMULTIPLE

Dear Gurus,

We have a customer request to upload massive billing documents with the reference of Outbound Delivery Documents. You can see below the BAPI we use:

BAPI_BILLINGDOC_CREATEMULTIPLE

However, there are several bugs we could not find solutions. The document is processed once, and later same reference document ends up with errors as they are being processed. We use a certain case to test the upload process and same case gives different outcomes as below:

Scenario 1

Doc No 9*1 saved (no accounting document generated)

Doc No 9*2 saved (no accounting document generated)

Doc No 9*3 saved (no accounting document generated)

Doc No 9*4 saved (no accounting document generated)

Doc No 9*5 saved (no accounting document generated)

Doc No 9*6 saved (no accounting document generated)

##Documents posted in Scenario 1 are reversed for next test process##

Scenario 2

Doc No 9*7 saved (no accounting document generated)

Doc No 8*1 is currently being processed.

Doc No 9*8 saved (no accounting document generated)

Doc No 9*9 saved (no accounting document generated)

Doc No 8*2 is currently being processed.

Doc No 9*10 saved (no accounting document generated)

As it is shown above, results are different despite of the same testing sample.

Kindly asking you to give a solution for this incident or a note to implement if available.

Thanks in advance for your support!