This solution worked on my 3647. Nice job DellFarmer!
DellFarmer is right: Dell needs to come up with a uninstaller so you don't have to use a third party utility to perform a deep scrub of the registry and files.
So after trying Dellfarmer's fix, it worked for me as well. I just had to make sure I really got in there and cleared all those registry files. Hopefully there won't be problems in the future like this when trying to update SupportAssist.
Thank you DellFarmer. After weeks of trying every workaround, DellFarmer's answer solved my issue. (see page two of this thread!) Anyone on this thread looking for the answer that gentleman has it! Do it!
I'm also having issues with the Dell Assist software. It's not going past the initial "loading pc optimization tools". I tried downloading the installer again but it still stuck. I tried repairing the software and some file is missing.
My laptop is XPS 15 9560