Q: Reinstall of Time Machine backup won't finish

I made the mistake of upgrading to Sierra and it killed some of my apps that I use on a daily basis. I'm in the process of downgrading back to El Capitan. I've successfully reinstalled El Capitan and am trying to reload a Time Machine backup from before I upgraded. I'm using the Command-R method after restarting and selecting Restore from Time Machine Backup in the OS X Utilities selector. Everything goes smoothly until about an hour into the 13-hour calculated restore. At that point my iMac restarts on it own without finishing and ends up at the login screen. I click my profile and it starts the setup process by asking me for my Apple ID and password but keeps telling me that my ID and password are wrong. I know what I'm entering is correct because I logged on to this forum. So I skip that step (because there's nothing else I can do) and end up at my Desktop where clearly no apps or settings or anything has been restored. Please help. My digital life, and finances are quickly falling behind.