I wish that I found the solution earlier, but I am not sure if I have a different solution or if it's just the servers that I downloaded from were just slow. I tried the temp folder and cleared that out and I also tried the wsreset.exe command.... nothing. I have two laptops: both almost identical, except for the software on them (manufactor drivers are the same). First laptop: no issue. Second laptop: 0% downloaded almost all the time. I had various error numbers. If I remember correctly, the most common error for me was 0x800872EE2.
If any of these things I tried worked for certain, I don't know: I removed device drivers for a USB TV tuner (the device was never plugged in) and I also downloaded the optional updates, I think it were the "important" updates. I usually just get the security updates normally. The important updates did fail, but would be installed in steps eventually.
If I had fast startup enabled, I don't know. I never changed that and really didn't care about the startup speed since it seemed good to me. It's when I got that "START" button on 8.1, I was so happy - less steps finally to turn the laptop off.
I hope that this helps someone because I have been trying to update for almost a week now. When the download goes, it goes rather quickly (that of course depends on your ISP).