PHP notices about missing feed

We are getting these notices in our log:
PHP Notice: A feed could not be found at https://thomasgriffin.io/sitemap_index.xml. This does not appear to be a valid RSS or Atom feed. in /home/user/wordpress/wp-includes/class-simplepie.php on line 1391
… and have traced this back to soliloquy-lite/includes/admin/utils.php line 85. An update with a revised URL would be appreciated. Thanks.