Inconsistent update serial number with WS_DELIVERY_UPDATE

Dear all,

We are having an issue when using this FM however it's not officially supported by SAP so I'd like to consult our community. I found some very old posts with the same issue but didn't get a solution so I thought of posting it again. Basically our issue is same as what he described, sometimes only 10 out of 12 serial numbers are getting saved in the delivery however there is no return message from the FM. He has mentioned the issue is with the locking of serial numbers, how do we know if there is such an issue during update? In general, how to make sure all serials are saved in the delivery?

https://answers.sap.com/questions/7992349/wsdeliveryudpate-for-serial-number.html