What ever came of this issue?
I believe I'm having the same problem.
A few downloads recently have stayed 'Downloading' forever, with no network traffic.
I've got one right now showing 5 files remaining with 6MB total left to download out of ~4.75GB
web-client shows it's only tried the articles on the main server, no activity on the backup servers.
It just sits there 'downloading' but seems to do absolutely nothing.
Doesn't look like anything special shows up in logs or messages.
I have to result to forcing downloading tall the par2 files, see if I have enough parts, even with the ~5 files incomplete, if I do, I delete these incomplete files from the download queue, so NZBGet moves on to the repair stage.
regardless, thanks again hugbug for all your work!