You’ve used full URLs for your Facebook and Google Plus links but not for Twitter. You can change it in Users > Your Profile.
I currently don’t see the author social fields in my test sites but maybe it’s just on my end. I’m currently investigating.
If you don’t see the fields also, you will need to update the Twitter link via functions.php. The code you will put in your functions.php for ONE TIME ONLY is this:
add_user_meta( 5, 'twitter', 'http://twitter.com');
5 is the user id. You can get your user ID by following this third party article https://rudrastyh.com/wordpress/get-user-id.html
Change the Twitter URL with the Full URL of your Twitter profile.
After it’s updated, remove the code.
Hope that helps.