Based on feedback, the following problem seems to be also rather popular:
The Facebook Login button is displayed several times (2-3)Affected:Websites that have additional FB related modules or scripts
Solution:Make sure that no other FB related module or script in your website has the following line of code inside
e.src = document.location.protocol + '//connect.facebook.net/......./all.js';
OR
<script type="text/javascript" src=".....//connect.facebook.net/...../all.js"></script>
Dots mean any number of character combinations, code can be similar and not EXACTLY the same as the one presented.