Assuming it’s the same issue as you’ve just posted about here (which would make this double posting, something that’s not really appreciated), have you checked the answer I’ve given there?
using --serial instead of --dfu gives less output. Technically, the flash was correct, but the Electron won’t run it since it’s compiled for the wrong platform. Try the suggestion I’ve pointed you to in the other topic to see if that works.
alternatively, compile your software in the CLI using particle compile electron [path to directory]