Thanks for reporting back. I think the LOO is catching all error message after we recently change the logging system. I have a PR to fix this but it still needed more work.
As for the effect_n error, they are caused by the Deterministic RVs in your model. For example, if you do the trace plot of Exponential model VA is a flat line. I think we should improve the warning system to catch warning only for the Free RVs. For now you can try doing VA = data['A'] * self._df(k, data['DA']).