MarketPress issue with Squirrly SEO 2018 (Steve) plugin

After activation "Squirrly SEO 2018 (Steve) plugin products pages start display this error:
Fatal error: Cannot use object of type WP_Error as array in /wp-content/plugins/squirrly-seo/models/Frontend.php on line 373

Witch is:

if (!empty($cat) && count($cat) > 0) {
$post->category = $cat[0]->name; // 373 line here
if (isset($cat[0]->description)) $post->category_description = $cat[0]->description;
}