This is most likely because the WordPress theme you’re using has responsive video functionality built into it which is conflicting with the responsive video functionality built into the Custom Facebook Feed plugin. To resolve this try adding either of the following two JavaScript code snippets to your site. This can be done manually using a custom JavaScript plugin. For further information see our documentation here.
setTimeout(function(){ $('.cff-iframe-wrap iframe').unwrap(); }, 500);
OR
setTimeout(function(){
$('.cff-iframe-wrap iframe').each(function(){
if( $(this).parent().hasClass('fluid-width-video-wrapper') ) $(this).unwrap().wrap('<div style="float: left; width: 100%;"></div>');
});
}, 500);
If you’re still experiencing an issue then please contact support and include a link to the page on your site where you’re displaying the feed.