Take another look for CityStrides added to your Home Screen somewhere, even if you think you don’t have to.
In my experience so far, that’s the most likely cause. When the logins go sideways like this, having that “app” PWA installed keeps the login broken.
The second most likely cause is the browser data for both domains not being fully deleted.
Outside of that 
I’d try another run through of the exact process noted in Resolving common login issues …