Billing job is Skipping few Deliveries

Hi Gurus,

Did any one came across this kind of issue?

Billing Job SDBILLDI Runs couples of times a day (for every 5 mints,10,15). It pick's up all deliveries and creates Billing.

But this job once in 2 months or 3 months, it is missing few deliveries, it skips.

For example.

1) Dealers creates 5 sales orders on Monday and got confirmed and deliveries got created and PGI is done.

2)This deliveries are ready for Billing

3)Billing job runs on Monday evening and picks 2 deliveries and created billing

4)But it skips 3 deliveries

5)Again Next day I--e Tuesday the billing job picks those 3 deliveries and creates Billing .

6)In few cases it won't pick those 3 deliveries and we manually doing with Vf01.

7) Up to now we are facing it for 4 dealers (Italy, France, Germany and UK)

Every time Dealers  tells he had not received few invoices(3).

Its Normal process and its delivery related .

Any SAP Notes?. Why system behaves in this way?

Thanks,

Seegal SK.