Could not find a valid session key when submitting Petition
Have been able to get over the session key error by installing a fresh install of WP and CiviCRM, then restoring Wordpress and CiviCRM DBs, repointing wp_config.php and CiviCRM.settings.php. Also had to rename my table prefixes in wp_config.php to match my restored tables. The caches get created once you start up CiviCRM and do things. Testing so far all functionality is working again. Hopefully this may help someone should you come across this issue which is pretty horrible.