Hi Coen,
Welcome to Qsm Pro Support Forum. Hope you are having a great day.
The %CATEGORY_SCORE_X% is working as per requirements. The variable checks for the percentage of the correct answers, the user has provided. So, the quiz must be graded as Corect/Incorrect based and not Points based.
You can also check the following sample quiz here: https://support-qsm.expresstech.dev/quiz/category-score-check/
However, %CATEGORY_POINTS_X% works on the basis of points added for particular answers. So this variable works for Points based graded quizzes. If you want to add the points of given answers per category, this variable will fulfill your issue.
Regards,
Kriti