I am getting a broken/blank image for the avatar's of the users created using this plugin. I believe this is because you are using a url to pull the twitter profile images that is no longer valid in the Twitter API v1.1. Here is the setting in nextend-twitter-connect/nextend-twitter-connect.php:
update_user_meta($ID, 'twitter_profile_picture', 'https://api.twitter.com/1.1/users/profile_image?user_id=' . $resp->id . '&size=bigger');
The url referenced is no longer valid. As far as I know (having used this API call on a different, non-WP site), you have to access the users/show API call and pull the profile_image_url value that is returned amongst the other json data.
As is, this makes the plugin unusable. Which, admittedly, confuses me as it seems to be actively used by many.