MS Access After Update Event not executing Update Query

Question

I have a quantity control in a form with the following code:

PublicOldQuantity As Long

Private Sub Quantity_GotFocus()

    If IsNull(Quantity.Value) Then
        OldQuantity = 0
    Else
        OldQuantity = Quantity.Value
    End If

End Sub

Private Sub Quantity_AfterUpdate()

    Dim ProductID As Long
    Dim NewQuantity As Long
    Dim db As DAO.Database
    Dim strSQL As String

    ProductID = Me.ProductID.Value
    NewQuantity = Quantity.Value - OldQuantity
            
    Set db = CurrentDb
    strSQL = "UPDATE ProductT SET StockLVL = StockLVL - " & NewQuantity & " WHERE ID = " & ProductID
    db.Execute strSQL
    Set db = Nothing
    
    Me.Requery

End Sub

I use pretty much the same Code in another form, just on a button and not in a after update event and it's working perfectly there. Here the query doesn't execute.

The same Query executed manually perfectly updates the StockLVL in the ProductT. Even writing the query as a separate Sub and calling that in the Event doesn't do anything. Also writing the query as a QueryDef Object with Parameters and calling that didn't work. I checked Parameters via Debug.Print and everything seems to be fine, the query just doesn't execute or at least the StockLVL Value in the ProductT doesn't update