Because the CSS of the primary theme (to v10.1.6) overrides the font-family in the `.widget-area .widget a` section of style.css (see below), none of the genericons for the social media sites will display when using the JetPack Social Icons Widget.

<blockquote>
/*--------------------------------------------------------------
Fallback CSS for Customizer Library Styles
--------------------------------------------------------------*/
`body,
.widget-area .widget a {
color: #3C3C3C;
font-family: 'Open Sans', sans-serif;
}`
</blockquote>

This behavior can be fixed by including the following code (best to do it in a <a href="https://codex.wordpress.org/Child_Themes" target="_blank">child theme</a>) instead:

`.widget-area .widget a {
color: #3C3C3C;
font-family: Genericons;
font-size: 2.5em;
margin: .10em;
}`

If you don't have a child-theme it can probably be fixed (without other erros/issues) by removing the line: `font-family: 'Open Sans', sans-serif;`.

Hopefully Kaira will include a fix in an upcoming release.