Group level credible intervals hierarchical linear regression

Questions
2 
        mu_a = pm.Normal('mu_a', mu=0., sigma=1)
        sigma_a = pm.HalfCauchy('sigma_a', beta=5)
        mu_b = pm.Normal('mu_b', mu=0., sigma=1)
        sigma_b = pm.HalfCauchy('sigma_b', beta=5)

those aren’t used in your model, did you forget them when switching between centered and non-centered?