When rating items in ArcGIS Online, the number of stars is sometimes added or deducted by one star.
Last Published: December 3, 2015ArcGIS Online
Bug ID Number
November 18, 2015
August 21, 2020
After review by the development team, it has been determined that this issue is related to a known limitation with the software that lies outside of Esri's control. The issue's Additional Information section may contain further explanation.
This is as designed. We have that documented in help too. Here is a link