We are also having issues with the Product quantity metric in Looker Studio. The Product quantity for each Product name and each Order ID is correct, but the total is way wrong (see attached image). It seems that the total Product quantity is adding the unique product quantity values (4 + 2 + 1 = 7).
When creating this same table in Piwik PRO the Sum of product quantity (Order) gives the correct total value = 21.
