I know you are working on it, but there was similar problem before, so maybe this is related to core.
Installed latest version, run update to 1.6.
#0 e_array->unserialize() called at [***\e107_handlers\e107_class.php:1791]
#1 e107::unserialize() called at [***\e107_plugins\metatag\includes\metatag.class.php:2957]
#2 metatag->getDefaultMetaTagsByType() called at [***\e107_plugins\metatag\includes\metatag.class.php:2865]
$data = array (
'title' => '',
'description' => '',
'abstract' => '',
'keywords' => '',
'news_keywords' => '',
'standout' => '',
'rating' => '',
'referrer' => '',
'generator' => '',
'rights' => '',
'image_src' => '',
'canonical' => '',
'shortlink' => '',
'publisher' => '',
'author' => '',
'original-source' => '',
'prev' => '',
'next' => '',
'geo.position' => '',
'geo.placename' => '',
'geo.region' => '',
'icbm' => '',
'refresh' => '',
'og:site_name' => '',
'og:type' => '',
'og:url' => '',
'og:title' => '',
'og:determiner' => '',
'og:description' => '',
'og:updated_time' => '',
'og:see_also' => '',
'og:image' => '',
'og:image:url' => '',
'og:image:secure_url' => '',
'og:image:type' => '',
'og:image:width' => '',
'og:image:height' => '',
'og:latitude' => '',
'og:longitude' => '',
'og:street_address' => '',
'og:locality' => '',
'og:region' => '',
'og:postal_code' => '',
'og:country_name' => '',
'og:email' => '',
'og:phone_number' => '',
'og:fax_number' => '',
'og:locale' => '',
'og:locale:alternate' => '',
'article:author' => '',
'article:publisher' => '',
'article:section' => '',
'article:tag' => '',
'article:published_time' => '',
'article:modified_time' => '',
'article:expiration_time' => '',
'profile:first_name' => '',
'profile:last_name' => '',
'profile:username' => 'admin',
'profile:gender' => '',
'og:audio' => '',
'og:audio:secure_url' => '',
'og:audio:type' => '',
'book:author' => '',
'book:isbn' => '',
'book:release_date' => '',
'book:tag' => '',
'og:video:url' => '',
'og:video:secure_url' => '',
'og:video:width' => '',
'og:video:height' => '',
'og:video:type' => '',
'video:actor' => '',
'video:actor:role' => '',
'video:director' => '',
'video:writer' => '',
'video:duration' => '',
'video:release_date' => '',
'video:tag' => '',
'video:series' => '',
'fb:admins' => '',
'fb:app_id' => '',
'twitter:card' => '',
'twitter:site:id' => '',
'twitter:creator' => '',
'twitter:creator:id' => '',
'twitter:url' => '',
'twitter:title' => '',
'twitter:description' => '',
'twitter:image' => '',
'twitter:image:width' => '',
'twitter:image:height' => '',
'twitter:image:alt' => '',
'twitter:image0' => '',
'twitter:image1' => '',
'twitter:image2' => '',
'twitter:image3' => '',
'twitter:player' => '',
'twitter:player:width' => '',
'twitter:player:height' => '',
'twitter:player:stream' => '',
'twitter:player:stream:content_type' => '',
'twitter:app:country' => '',
'twitter:app:name:iphone' => '',
'twitter:app:id:iphone' => '',
'twitter:app:url:iphone' => '',
'twitter:app:name:ipad' => '',
'twitter:app:id:ipad' => '',
'twitter:app:url:ipad' => '',
'twitter:app:name:googleplay' => '',
'twitter:app:id:googleplay' => '',
'twitter:app:url:googleplay' => '',
'twitter:label1' => '',
'twitter:data1' => '',
'twitter:label2' => '',
'twitter:data2' => '',
'dcterms.title' => '',
'dcterms.creator' => '',
'dcterms.subject' => '',
'dcterms.description' => '',
'dcterms.publisher' => '',
'dcterms.contributor' => '',
'dcterms.date' => '',
'dcterms.type' => '',
'dcterms.format' => '',
'dcterms.identifier' => '',
'dcterms.source' => '',
'dcterms.language' => '',
'dcterms.relation' => '',
'dcterms.coverage' => '',
'dcterms.rights' => '',
'itemprop:name' => '',
'itemprop:description' => '',
'itemprop:image' => '',
);