Outbound delivery confirmation (OBDLV_CONFIRM) with missing Handling Unit

We have a decentralized Warehouse LES (ECC6) with handling unit (HU) management with an idoc interface to our ERP (4.6C).

When we do a goods issue the HU information is sent to ERP in the SHP_OBDLV_CONFIRM_DECENTRAL segment E1BPDLVHDUNITM.

In some cases (<0.1% of idocs) we have issues with the HU data. The HU information is present and correct in the outbound delivery. In all other cases everything works fine.

Idoc error "Packed quantity is zero" In this case the packed quantity (PACK_QTY) and unit of measure (SALES_UNIT, SALES_UNIT_ISO) are not filled when the idoc is created in WMS.

How can i find the cause of the problem?

Note 877728 - "No qty spec for APM in confirmation" does not apply, the problem occurs at the dWMS side, not at ERP