Your Drupal site is triggering warnings that mention igbinary, similar to (but not limited to) the following:
Warning: igbinary_unserialize_header: unsupported version: [NUMBER], should be [...]
Warning: igbinary_unserialize_header: unsupported version: "[STRING]"..., should begin with [...]
Warning: igbinary_unserialize_zval: unknown type [...]
Warning: igbinary_unserialize_chararray: end-of-data in [...]
Add this configuration in the Memcache section of your site's settings.php file:
// Force memcache to use PHP's core serialize functions $conf['memcache_serialize'] = 'serialize';
Later versions of the Memcache module default to using the igbinary serializer, however, within Acquia Cloud the best practice is to use the PHP native serializer.