Serials do not attach to Order when Confirmed

-- HikaShop version -- : 3.2
-- HikaSerial version -- : 2.0
-- Joomla version -- : 3.7.5
-- PHP version -- : 5.6.30

I have set up three packs, each with a pre-defined list of serial numbers. The packs show which products they are assigned to.

I have placed a back end test order, added the product, then confirmed. After confirming, refreshed the page.

No serial number is being assigned to the order. It doesn't seem to be pulling serials off of the list. I tried it with the packs assigned to variants and also assigned ONLY to the master product.

I can't figure out what I have done wrong, but it just doesn't work. What do I do?

Jerome wrote: Yes, the serial association cannot work with products added manually in the backend since it does not use the order creation triggers.That's why there is a "refresh" button available in the backend interface while displaying the order details ; it allows you to ask for a refresh of serial association when the order has been manually modified.,

Does this mean that to use a stack of serial numbers, each order has to be refreshed manually to add the serial number to the order?

Also (just tested it), it seems that serial numbers taken from 'the pile' are random. They don't simply take the first available serial by ID. Or is there a way to force the 'order'?