If no file is uploaded for a product at the time an order is processed, no link will be issued for that item. And thus there will be no download link to re-activate in the Transaction Log.
Going forward we would recommend making sure a product has a download file uploaded prior to offering it to buyers to help avoid confusion.
To provide your current buyers with the files they purchased you can generate free links & send those manually under Manage Buyers > Send Free Download Link/Code.
Note we had to disable the email-sending function of our Send Free Download Link/Code feature, due to abuse by spammers.
However, you can still use this feature to generate free links, then just copy the link generated there and paste that into a personal message to each recipient. Note you can simply right-click on that link URL (or on a Mac, hold the Control key when you click) and then select Copy Link, rather than having to drag-select the URL manually to copy it.