Hello.
My site has the same symptoms as yours.
I was able to fix it by customizing the css of the icons. Please try it.
.yith-wcwl-icon.fa.fa-heart-o {
font-family: 'FontAwesome';
}
I figured it was probably because the Font Awesome css style loaded by the plugin is the latest version 5, but the <i> is version 4.
