Hi,
It would have been great if you could provide an example.
Then, let's take an example with the latest order D1K8M05.
In it, as you can see, you have only one product:
monosnap.com/file/Ya8UhSVVm7XYH7F2VqG5zxgHJF75cT
And a serial is attached to the order and no after purchase download link is available, like you describe. However, that's totally normal.
If you look at the settings of that product, you can see this:
monosnap.com/file/XsDIf93afueI6616x0GLpRhntmfWDc
The only file attached to that product is a "free download" and thus the download link is on the product details page on the frontend and there is no download link available to the customer after the purchase. If that's not what you want, then you should edit the file and turn off the "free purchase" setting.
And similarily, you've added a serial pack to the product:
monosnap.com/file/lKLP5WohwVd1RAuG0TGlNqYKISw0HF
So it's normal that a serial is attached to the orders of that product.
So basically, I still don't see what is the problem. HikaShop is only doing what you configured it to do, at least for that order.
I don't see how that could have suddenly changed unless you changed these product settings yourself.