When symbology based on text fields have the same values represented in different cases, for example, upper case or lower case or both, ArcGIS Online does not display symbology for features when switching from single to unique symbols.
Last Published: January 20, 2015ArcGIS Online
Bug ID Number
October 29, 2014
March 30, 2022
Operating System Version
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.
At the rendering time, these values are case sensitive. So, ArcGIS Server Map/ Feature Services would return multiple value for those values.
If users have attributes like 'KMS', 'kms', or 'Kms' in a field, they must change it to 'KMS_1', 'kms_2', 'Kms_3' to make them unique.