Error

When you unenrol a user from a course with an assignment in it, you get an error modal.

Stack trace:

SyntaxError: Unexpected token 'T', "The instan"... is not valid JSON
    at parse (<anonymous>)
    at https://clean.m41.dev4.3072.ru/lib/javascript.php/1693468035/lib/jquery/jquery-3.6.1.min.js:2:79614
    at l (https://clean.m41.dev4.3072.ru/lib/javascript.php/1693468035/lib/jquery/jquery-3.6.1.min.js:2:79731)
    at XMLHttpRequest.<anonymous> (https://clean.m41.dev4.3072.ru/lib/javascript.php/1693468035/lib/jquery/jquery-3.6.1.min.js:2:82499)

The problem is in "The instance of this module does not exist" prepending JSON.
The error string id is 'moduleinstancedoesnotexist' in 'core_error'.
mtrace in /lib/grade/grade_item.php line 2588

Steps

• Create a course.
• Add an assignment activity.
• Enroll a user (student).
• Hand in the assignment using the student account (probably optional).
• Grade the assignment (probably optional).
• Disable Assignment activity in "Manage activities".
• Unenrol the student.

We have encountered the same error with another activity (not in the core) in another Moodle site. The same problem is probably relevant to other gradeable activities as well.