When making multiple requests to a map service with the returnAdvancedSymbols property being true, non-ASCII characters are incorrectly encoded in responses after the initial request after installing ArcGIS Server Security 2023 Update 1 Patch (July 20, 2023).
This defect is resolved in the ArcGIS Server 11.1 Map Service and Custom Data Feeds Patch. This patch is available for download at https://support.esri.com/en-us/patches-updates/2023/arcgis-server-11-1-map-service-and-custom-data-feeds-patch.