Thanks for providing a backup of your Lesson.
It's working correctly on my Moodle test site. However, with DEBUG mode ON I can see some error messages like:
Incorrect scale id: 38
line 1021 of \lib\grade\grade_item.php: call to debugging()
line 843 of \lib\gradelib.php: call to grade_item->load_scale()
line 796 of \lib\gradelib.php: call to grade_format_gradevalue_real()
line 535 of \lib\gradelib.php: call to grade_format_gradevalue()
line 3630 of \mod\lesson\locallib.php: call to grade_get_grades()
line 265 of \mod\lesson\view.php: call to lesson->process_eol_page()
Maybe due to the fact that in your Lesson Settings you selected Grade: Scale: Default competence scale (and I do not have your Scales system installed on my test site?).
When exactly do you see the error message you reported "Exception : Attempt to assign property "response" on bool"? Screenshots please.
I see your lesson is written in French. If you like you could re-post this discussion to the French speaking forum, where you will be able to get answers in French.