Hi winbytwo ,
Welcome to the forums!
There could be another Font Awesome script in your site causing it to show as a rectangle. Perhaps a theme or another plugin. 🤔
You could try to add this script into your site, making Font Awesome 5 and Font Awesome 4 compatible with each other.
<link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.13.0/css/v4-shims.css">
Another reason it could turn into a rectangle is that the font-weight of the icon is being changed.
If adding the script doesn't work for you, could you perhaps share us a link to your site?
We would like to take a look and find out what's causing the issue.