The recent Garmin auth changes have caused problems for some people. The PWA (site saved to the Home Screen as an app) seems to be the biggest problem, but it’s pretty simple to fix up.
I’ve been getting this question enough that it was worth a Wiki entry: Resolving common login issues
(It looks like you’re currently logged in through Strava … if you can update that account’s email to your real email – but add “+citystrides” into the user, like myemail+citystrides@gmail.com or whatever – I can merge the two accounts for you.)
Let me know how that info helps!
Hm, yeah, I don’t state why there was a problem 
The four possibilities are either a blank form, the invisible honeypot field being filled in (very unlikely you managed that lol), an invalid email, or getting the math problem wrong.
I’ll look into getting that to be more descriptive..