Costing = Real Time, Inventory Valuation = Real Time (automatic), "Real Price" or "Average" costing in purchase setting is turned on. 

Stock In/Out, Stock Valuation, Stock Journal, Income/Expense accounts are all filled out in the category, I left it blank in the actual product .  

Sometimes (or should I say most of the times) the product doesn't not update correctly with the new product cost, it stays 0.

At absolutely random times to me, the product does correctly show the cost, I have not been able to pinpoint  exact issues as I follow the exact the same procedure every time. Which is:

Create PO>in PO, create Product according to settings above> Validate PO>Transfer Inventory>Validate Invoice 

Thank you for taking your time to take a look at my question.