I think I found an issue with the UI in the metadata plots, here is the asset code to reproduce:

@asset
def random_integers(context) -> Output[DataFrame]:
    df = DataFrame(
        {
            "x": random.randint(1, 10, size=random.randint(1, 100)),
        }
    )

    return Output(df, metadata={"num_rows": df.shape[0]})