Steam download resetting to 0GB progress after restart

I've seen this issue come up pretty frequently lately. But the good news is there is a work around.

You'll need to check for the "Local Content" of the game in your Steam Library folder. If these files are here and are relatively the same size as your downloaded portion (9 GB) you should be able to recover them by moving the files from your steam downloading folder to your steam common folder and restarting steam. This will force steam to try to install the game, realize the game isn't finishing downloading, and fetch the remaining pieces.

Here's more detail instructions for doing so