Upon further investigation with WP debug:
Notice: Undefined index: wpar_more_details_btn_value in /var/www/wp-content/plugins/author-hreview/inc/review_meta_box.php on line 20 Notice: Undefined variable: wp_cache_object_cache in /var/www/wp-content/plugins/wp-super-cache/wp-cache-phase2.php on line 1106 Notice: Use of undefined constant CURLOPT_URL – assumed ‘CURLOPT_URL’ in /var/www/wp-content/plugins/pubsubhubbub/pubsubhubbub-php/publisher.php on line 68 Notice: Use of undefined constant CURLOPT_POST – assumed ‘CURLOPT_POST’ in /var/www/wp-content/plugins/pubsubhubbub/pubsubhubbub-php/publisher.php on line 69 Notice: Use of undefined constant CURLOPT_POSTFIELDS – assumed ‘CURLOPT_POSTFIELDS’ in /var/www/wp-content/plugins/pubsubhubbub/pubsubhubbub-php/publisher.php on line 70 Notice: Use of undefined constant CURLOPT_RETURNTRANSFER – assumed ‘CURLOPT_RETURNTRANSFER’ in /var/www/wp-content/plugins/pubsubhubbub/pubsubhubbub-php/publisher.php on line 71 Notice: Use of undefined constant CURLOPT_USERAGENT – assumed ‘CURLOPT_USERAGENT’ in /var/www/wp-content/plugins/pubsubhubbub/pubsubhubbub-php/publisher.php on line 72 Fatal error: Call to undefined function curl_init() in /var/www/wp-content/plugins/pubsubhubbub/pubsubhubbub-php/publisher.php on line 74
We fixed this by adding support for curl in PHP. The last fatal error was a strong indication.
