Form submission emails not sending to email address in CC field

Hi,

I've noticed that form data email responses after a form has been filled out and submitted aren't sending to email addresses that have been entered in the CC field.

The form data email is being successfully received to the email address stated in the 'To' field oddly!

Any reason as to why this would be and any potential solution? It only seems like a week or so again it's stopped sending emails to CC'd email addresses.

Thanks.