reCAPTCHA v2 not loading sometimes in some browsers

Hi, We are doing some work for a customer and they complain about the captcha not loading, sometimes, in different browsers (Firefox 36.0.1, IE11). I cannot replicate this issue from my machine, does anyone know a potential reason? Maybe network problems? Thanks, -- You received this message because you are subscribed to the Google Groups "reCAPTCHA" group. To unsubscribe from this group and stop receiving emails from it, send an email to recaptcha+unsubscribe@googlegroups.com. To post to this group, send email to recaptcha@googlegroups.com. Visit this group at http://bit.ly/1dkFnYd. For more options, visit http://bit.ly/P65DvS.