Strange, know your OS/Browser combo? I've had issues with it before in areas with poor connectivity, since it requires making API calls off to Google (after the page has loaded). The button should start the whole reCAPTCHA flow, but I've noticed it's not 100%.
Android 5.0.1, Brave browser. I tried disabling the tracking protection, but it still did nothing. Connectivity shouldn't be a problem, because I'm using my WiFi right now.
Edit: nevermind, it works now. Maybe I was too impatient before.