There are two problems with the course participants filter when used inside a course (as opposed to the site front page):

1. The conditional for checking the current course is wrong (as described in MDL-75536);
2. The generated SQL for determining whether a user had never accessed a course was wrong (because the user_lastaccess record would not exist at all, so the Never option was broken as described in MDL-71088)

Original report

Open file - /user/classes/output/participants_filter.php, go to get_accesssince_filter() method.

1) Condition is incorrect - "if (!$this->course->id == SITEID)".

2) The condition for getting not active participants is incorrect:

$params = [

                'courseid' => $this->course->id,

                'timeaccess' => 0,

            ];

In this case, rows with "timeaccess=0" condition do not exist. Need to change condition, for example, use join with tables {user_enrolments}, {enrol}

We noticed a problem when we tried to select course participants due to "Inactivity for more than Never"