Check following settings for auto evaluate quizzes:
1. Quiz is set on auto evaluate mode in Quiz Settings
2. Comments are enabled for all the questions in the quiz
3. The question types in the quiz are selected in WPLMS options panel->Course Manager->Auto Evaluate question types
4. Discussion settings are set as per documentation. : http://prntscr.com/nou6f3
Still not working then please try adding this given code in your wplms-customizer.php file in wplms customizer plugin :
add_filter('wplms_get_answer_object_meta_query',function($settins){
unset($settins['meta_query']);
return $settins;
});