I have the same problem with the latest JDownloads.
My site is running via HTTPS and it's also forced in Joomla's server settings.
I get this really weird error in Chrome when trying to download a file:
Mixed Content: The site at '
https://i-war2.com/' was loaded over a secure connection, but the file at '
https://i-war2.com/...zip' was redirected through an insecure connection. This file should be served over HTTPS.
That's really weird, because both URLs start with HTTPS. So maybe there's another redirect in there Chrome doesn't like or something else...?
For now I've resorted to serving the files via PHP but some files are really big and might fail because of the execution time limit. Not an ideal solution.