The mainstream view is that the density calculations for all high density asteroids were measurement errors. 33 Polyhymnia was measured in 2012 in a study with many other asteroids. There is non-peer reviewed 2023 analysis of mass and density that indicates 12.35 grams per cc density for 33 Polyhymnia. There is the need for more and better telescope observations and measurements.

Here is the full paper in Arxiv.

One such rock is 33 Polyhymnia, located in the main asteroid belt between Mars and Jupiter. Scientists have long been puzzled by its density, as the 34-mile-wide (55 kilometers) object does not have the mass needed to squeeze minerals into ultradense forms.