Thank you Jurgen and Dave for the response.
Here's the original error message:
I ticked the decimal place as per unit and saw that the missing .002 TO is under the On-Order Stock Column, MB5T shows that this .002 TO Quantity is stock in transit. However, I think this is normal because the stock in transit columns only show those stocks involved in intercompany code transactions.
Here's the PO History as requested:
I'll do a thorough check of the MB51 movements and will get back if I find anything unusual, but at first glance everything seems about right, all 101s are matched with their respective POs and there's no unusual movements done with the stock in transit.
I also did simulate this scenario in our test boxes and I was able to post a GR.