You could try the advice in the bottom half of this page.
https://support.google.com/android-o...-1487517469408
It seems that a factory default leaves something behind, and that you need to go to recovery mode to get rid of it. It may be worth waiting the 24 hours that it suggests.
I'd appreciate it if you could tell me if it works, because the article may shed new light on a slightly different problem I'm having with Google log in.