Not at all surprising. ChatGPT ‘knows’ a course’s content insofar as it’s memorized the textbook and all the exam questions. Once you start asking it questions it’s never seen before (more likely for advanced topics that don’t have a billion study guides and tutorials for) it falls short, even for basic questions that’d just require a bit of additional logic.
Mind you, memorizing everything is impressive and can get you a degree, but when tasked with a new problem never seen before ChatGPT is completely inadequate.