I’m having the same issue (see warnings below). I do see the list of google fonts populated. Thanks for any help!
Warning: fopen(…/wp-content/plugins/shift8-full-navigation/components/cache/fonts.json): failed to open stream: No such file or directory in …/wp-content/plugins/shift8-full-navigation/components/functions.php on line 244
Warning: fwrite() expects parameter 1 to be resource, boolean given in …/wp-content/plugins/shift8-full-navigation/components/functions.php on line 245
Warning: fclose() expects parameter 1 to be resource, boolean given in …/wp-content/plugins/shift8-full-navigation/components/functions.php on line 246