Hi, I had a similar issue. My icons didn’t show up at all. They were there, because when I hover over with the mouse I could see there were some buttons.
I fixed it by installing the FontAwesome plugin and add the following code to Custom CSS. Don’t really like to install extra plugins (if it should work from the theme itself), but at least I can see the icons now.
.fa {
font-family: FontAwesome;
}
Maybe this works for you!