From the support forum, I see that this is a common issue. I have read pretty much all of them but have not found a solution. See image rl-font-awesome-icons.jpg.

1. My Font Awesome settings are correct, I believe. See screenshot.
2. I have added your code to my custom.scss file.
3. I do not have Solidres or JCH Optimized installed.
4. I have tried changing fontawesome to Font Awesome 5 Free, but no help.
ORIGINAL
.nav.mod-list li a:before {
content: "";
font-family: FontAwesome;
margin-right: 0.625rem;
}[/code]

CHANGED
.nav.mod-list li a:before {
content: "";
font-family: 'FONT AWESOME 5 FREE';
margin-right: 0.625rem;
}

I have supplied credentials if needed.

Thanks for your help, Ivo.