I am using public account for a hobby map. The clustered points appear correctly in Map Viewer Classic but wrong in the new Map Viewer. Only problem that I see is with clusters with 2 features. Single points and more than 2 points appear correct but 2 point clusters appear smaller than single points. This happens in web apps as well.
From MV Classic, where cluster with 2 points appears correctly larger than single points.
From New MV, the 2 point cluster is smaller than single points.