Product does not issue a link for its own uploaded file along with links for files bundled from other products
A product can use either Single File Download or Bundle Other Products, but not both at the same time—i.e., you cannot have a product that delivers file(s) from other products and also delivers a file uploaded to itself. Note how ticking the box to Bundle Other Products unticks the box for Single File Download, and vice-versa.
If you upload a file to a product with Single File Download enabled, and then later edit that product to enable Bundle Other Products, then that previously-uploaded file will become unavailable to issue to buyers that product, and it will also be unavailable to bundle with other products. Bundle Other Products can only be used to issue files uploaded to other products which have Single File Download enabled.
To resolve this, you can simply add a separate product (if you haven't already) for each and every Single File Download you want to issue in the bundle, then set up the bundle product you will actually sell to bundle all of those individual files, without also expecting the bundle product to issue any file of its own.