Why did my Steam download restart back to the beginning?

Steam does not track download progress if the computer shuts down. When you turn your computer back on, it will say that it is starting over from the beginning, but I believe it will check to see if it already has each file before it downloads it again. If it finds the file, it will move on to the next file instead of re-downloading it, so it should move through the download process much faster the second time as it is just finding all the files again until it gets back to where the download was previously.

In my opinion, it is best to leave your computer on until all downloads are completed, but it does not start over completely if you do pause the download or shut off your computer. It just takes a bit of time to figure out where it was before continuing the download and installation.

This happened to me once in the Epic Games Launcher for the fortnite update a couple of days ago.. Don't worry.. The game is really 90% downloaded and it is saying 0% because you 'shutdown' your PC. Steam will download the remaining 10% and shows the percentage of the download.

This also happened to me many times and from my observation, It happens when a game has a new update whilst downloading the game. This won't happen when you continuously download the game without restarting or shutting down your PC and even though the game releases a new update it will still continue to download until it finishes.