My initial thought is there is a bug somewhere along the pipeline that unpacks your dataframe to the pymc model. If it is possible to share your dataset, that might make it easier to locate so I can try your code locally.
Which object is the array([1. , 1.02083333, 1.04166667, 1.0625 , 1.08333333,\n 1.10416667, 1.125 , 1.14583333, 1.16666667, 1.1875 ,\n 1.20833333, 1.22916667])? I can’t quite tell from the error message but it looks like it’s pointing to test_month_idx which really should be integers.