On generation 1 tempaltes you can find the social icons dissapear after an upgrade. This is because they have broken the FontAwesome icon usage because thy have not included the libraries (or removed them).
Joomlashine Fix
To fix this add the following code
<script src="https://use.fontawesome.com/1f6d68dad8.js"></script>
into either of the the following places
- Edit the template index.php and add it right under the <head> tag
- Goto (Your Template)-->SEO & System --> Analytics code --> Put the code in above any analytics code
Alternative Fix
Using a 3rd Party Font Awesome extension such as NS Font Awesome - Joomla! Extension Directory would do the same by adding the FontAwesome library back in.