An Alternate ID was setup in Stock Item for UOM. Upon syncing the sales order, we found out that the UOM did not properly sync. (for specific order only)
As tested and simulated in another instance it worked perfectly.
Based on my initial checking through Audit History, I saw that the order created with these UOM
which is supposedly (from BigCommerce API order)
The first SKU was ordered 24 CS but created as 1EA and the other one was 1920CS and becomes 160PK
I also check the Audit History of Stock Item and I found nothing changes on its cross reference - alternate ID