Solving that problem is beyond the scope of this plugin’s support forum.
If you’re a Font Awesome Pro subscriber, you can get more support by emailing hello at fontawesome dot com.
A couple of quick tips for you, though: this plugin has a couple of features that can have the effect of solving problems whose symptoms can include icons not showing up:
1. Font Awesome version 4 pseudo-element compatibility: FA Kits have built-in help with this, and the plugin when loading Font Awesome from the CDN helps with this. It’s complicated to achieve without the extra magic in the plugin and/or the v4 compatibility built into Kits.
2. Removing conflicting versions of Font Awesome.
For this, you can find guidance in the docs on the Font Awesome web site for how to do it without the plugin.