Not sure if this is correct fix because there are no information about this change, but today sync (13.2) broke look of my site.

In theme.xml 

<library name="bootstrap" version="4" /> 
<library name="fontawesome" version="5" />

change to:

<library name="bootstrap" version="4" scope="front,admin,wysiwyg"/>
<library name="fontawesome" version="5" scope="front,admin,wysiwyg"/>

Not sure about settings, but without a scope, libraries are not loaded. 

This theme uses bootstrap4, so I know that it is not loaded in the admin area (although scope admin), and it is probably loaded in the TinyMCE area thanks WYSIWYG scope.  Not sure for now, I am not using the Tinymce4 plugin for now. 

Don't forget to clear cache, theme.xml is cached in the file.