Something changed in `pytensor > 2.12.3` (and thus `pymc > 5.6.1`) that makes my `pytensor.gradient.grad` call get stuck - any ideas?

That’s interesting… I remember you noting that elsewhere as a difference between v3 and v5. I’ve not wrapped my head around that yet!

I’ll try rvs_to_values on the y_c and y RVs and see what happens…