the best way to resolve the twitter problem is edit the file twitterfeed.js in the plugin editor. You have to remove the next line in the .error function:
alert("error: " + error);
And with regard to the mailchimp issue, when you select the option ‘Mailchimp form’ in the option ‘Email Subscriptions Type’ and nothing happens, doesn’t it? any message?
If you want, you can create a new user to me in your admin panel. It is faster if I can change the code for testing. I have done this with other users and there were no problems. You can trust me. I only want fix the problem. Send me the data to my email firstname.lastname@example.org