Hi @PedroSebe yes, I did try giving them the same shape, which did sample successfully.
My confusion then becomes, why does this logic not extend to the binary response case? If you see the first code block z_student has shape (1,students) while z_question has shape (questions,1).
These elements must be shaped in this way to ensure proper sampling. Yet, this rule does not extend to multi-class problem. And I’m not sure why. See: IRT w/ PyMC3, unusual number of parameters modeled?