Custom terrain RGB/hillshade

**mapbox-gl-js version**: 2.10.0

Hi,

We are trying to display our custom terrain / hillshade using RGB tiles. To do so, we went through the following procedure:

`gdalwarp -t_srs EPSG:3857 -dstnodata None -novshiftgrid -co TILED=YES -co COMPRESS=LZW -co BIGTIFF=IF_NEEDED -ts 18000 18000 -r lanczos -wo SOURCE_EXTRA=1000 SRTM.tif SRTM.3857.tif`

`rio rgbify -b -10000 -i 0.1 SRTM.3857.tif SRTM.3857.RGB.tif`

`gdal2tiles.py --zoom=0-12 --processes=8 --srcnodata=-32768 -x SRTM.3857.RGB.tif tiles/`

`mb-util --image_format=png --scheme=tms tiles/ terrain_rgb.mbtiles`

So, we ended up with a working MBTiles filled with RGB PNG files, though below the result is not satisfying as you can see different weird spots usually located at around 3000 meters height.

We tried the procedure with two different sources (SRTM and EUDEM) the result is the same.

Do you have any idea?

Thanks.


Start by reproducing the reported artifacts with mapbox-gl-js 2.10.0 and the generated RGB MBTiles from the GDAL, rio rgbify, and mb-util commands. Compare the terrain and hillshade output from both SRTM and EUDEM sources; done means identifying whether the spots come from tile generation or map rendering and documenting or fixing the cause.

Written by the indexing model from the issue text.