Hello Prabhat,
Can you try running transaction /SAPAPO/AC05 with the Product & location. It is more likely (as someone mentioned) inconsistency between the Live cache and APO DB. This transaction will show the list of Sales orders in Live Cache for that Product/location. If you are not able to see in this transaction also..I could think of only - Rejecting the Sales order and re-entering a new order? or removing the rejection....
Let us know.
Thanks,
Uthaman