Google reCaptcha reset doesn't work

The grecaptcha.reset() method accepts an optional widget_id parameter, and defaults to the first widget created if unspecified. A widget_id is returned from the grecaptcha.render() method for each widget created. So you need to store this id, and use it to reset that specific widget:

var widgetId = grecaptcha.render(container);
grecaptcha.reset(widgetId);

See here.