I have had this problem crop up numerous times. The recent software update certainly made downloads go faster again, but I'm still having this issue.
Essentially, I will queue up a bunch of shows that I want to download to my iPad (for watching on a airplane or when I have no/bad wifi connectivity, so streaming isn't an option). At first everything will go fine.
But at some point, the downloads will just stop. Whatever show it's on will just not download any more. the iPad thinks it is still downloading (at least, the icon stays as the pause icon [meaning it is the one currently being downloaded]), but nothing.
If you try to manually select another show farther in the queue, it will show "0.00 B of XXX GB. Calculating..." and just stay stuck on calculating.
I'm not sure if it will stay stuck like this forever. I have sometimes also seen a handful of the shows in queue showing as "download failed" and it looks like it's stuck on whatever one is next in queue, but I'm not sure if this is the same problem, just farther along in the process. I assume it probably is.
Sometimes, when I've seen this issue, I've been able to fix it by going back to Streaming setup and redone setup. Then I go back and restart the failed download and it starts right back up again. But sometimes this doesn't work (like right now). The setup goes fine, but the download still never starts.
I've tried deleting my whole queue, then restarting the app, then adding a show to download again, and it just stays stuck in the calculating step.
Anyone have any ideas? Rebooting the Roamio is the next step, but I'm in the middle of recording stuff now so don't want to interrupt that process. Plus, this seems to happen often enough that rebooting is not an acceptable long term solution.