Wrong unique values web map raster symbology

[ClémentLaskar]

Hi,

I have published an ImageService from a mosaïc on an ArcGIS Server (10.7). Original data are 4 bits GRID rasters.

The mosaic stores pixels values on 4 bits. Only values from 0-8 are used so I have max 9 unique values.

I add the raster to the map and then I want to symbolize it using unique values.

Here is the server response from the 'histograms' REST endpoint

All values seem to be present. Though the proposed symbology below shows 2 times the value 4 and doesn't shows the value 7

Has someone ever encountered this behavior ? How can it be fixed ?

Thanks !