I don't have a direct answer beyond my previous comment, but maybe looking at the code of the adaptable theme would you give you some insights about the nature of the problem:
Looking at the adaptable\classes\output\core\course_renderer.php file (starting at line 859), it seems that the participants count by adaptable is being done by using a function called course_participant_count() located in the adaptable\classes\utils.php file.
Seeing that the function checks for the mod/assign:submit capability, that's why asked about it previously.