Appearance – Customize – Custom CSS
Add the following:
.fa.fa-facebook, .fa.fa-twitter {
font-family: “Font Awesome 5 Brands”;
font-weight: 400;
font-size: 18px;
}
.fa.fa-adn, .fa.fa-bitbucket, .fa.fa-bitbucket-square, .fa.fa-dropbox, .fa.fa-flickr, .fa.fa-instagram, .fa.fa-stack-overflow {
font-family: “Font Awesome 5 Brands”;
font-weight: 400;
font-size: 18px;
}
.fa.fa-linkedin {
font-family: “Font Awesome 5 Brands”;
font-weight: 400;
font-size: 18px;
}
That fixed the issue.