OTM Cost Allocation not working as expected

Summary:

I have requirement to allocate the shipment cost on to orders. I have multistop shipment where i allocate the cost on the basis of volume carried distance.

When i try to allocate the cost without any update to order/shipment it works fine.

The catch is I do have specific business requirement wherein i need to update the ship unit count on order release (Shipment Tracking event actual pick quantity —» Order Ship Unit Count)-which i do by DSQL query. Once the above update is done on the Order's ship unit and then i allocate the cost then there is a mismatch in allocated cost based on volume carried distance metric.