Thank you, Ines! When I use my own model trained with "prodigy train", using ner.teach only shows scores of 1.00 from the very beginning.
If I use a prebuilt pipeline (en_core_web_trf), it will start with lower scores at first, but after displaying a sequence of examples with no entities (correctly), it will switch back to showing cases with entities, but all annotations will be wrong and all scores will be 1.00 going forward. I created a separate ticket about this latter case.