Hi,
Followed the instructions, found and deleted the Garmin cookie, reloaded CityStrides, and it still loops back to the sign-in page. Funnily enough, when I opened incognito mode to sign in to the forum to tell you this, incognito seemed to have remembered my credentials (i.e. I was already signed into the forum). So incognito is working wonderfully for my purposes, but I’m happy to continue trying stuff if it will help you figure this out. If it matters, I don’t have a Garmin device.
Thanks again for your help.