Hello,
As far as I'm aware, it's not really possible for us to detect if a download has failed when someone is downloading it from the website. It would be possible to do from the app, but we don't have any plans to do it. Especially since the app will automatically resume a interrupted download until it completes.
As for operating system analytics, if you provide different builds for each OS the you can see the individual counts per each file. Does this help?