Answering my own question, the luminaries on this forum have a fix for a similar-sounding problem and it works for me and my test site.
In summary edit the file head.php in the comprehensive google map plugin folder (i.e [your site]/wp-content/plugins/comprehensive-google-map-plugin/head.php)
Comment out line 45 and replace it with this almost identical one:
wp_enqueue_script('comprehensive-google-map-plugin', CGMP_PLUGIN_JS. '/cgmp.admin'.$minified.'.js', array('jquery', 'wp-ajax-response'), CGMP_VERSION, true);
Kevin