I have the same issue.
I get error when trying to upload via Catalog-downloads
I did try to upload FTP, but when trying to create the product, in the field where you select the file, the file is not there. It's only the PDF test file I had done before.
I know it should see it, because when trying to re-upload using the catalog-downloads, I did the "overwrite existing file" and it sees the file as existing.
NVM, it works. It just was confusing in the creation of the new download. In my mind, the "select a file" was connected to the "overwirte existing file" in the checkbox above, as in "select the file you want overwritten" not "select the file to create the download"