What would be required for positive doubt?
There must be actual proof or reliable testimony that something invalidating occurred. It can’t be something that you think may have happened, that would be a negative doubt. For example, if a credible person who was there, at the consecration, testified that the proper matter or form was
not used, that would be a positive doubt. If someone conjectures that the bishop must be crazy for doing a certain consecration, that is a negative doubt.