Today, I noticed my Echo ring lights on and spinning for no apparent reason. So I just pulled the plug when I got no response. I quicly realized afterward it was most likely installing the new firmware, so not a good idea to unplug it.
I plugged it back in and it did this again as when booting up. I checked the app and sure enough the new FW was installed (it was not as of yesterday.) So, I probably turned off the Echo while it was rebooting after the upgrade was installed. (I sure hope so.)
The Take Away: If you see this happening to your Echo or Dot, remain calm, wait to see if it is finished in a minute or two and then check the app for the new firmware. I was lucky that I did not disturb the upgrade any earlier.
I hate auto updates for this reason, and why I don't allow Windows to do auto updates.