gdal2tiles QGIS 3.10 not referenced properly

I processed virtual rasters with gdal2tiles. The output seems reasonable and it is displayed correctly on the generated output maps (Leaflet, Openlayers, Google). I then copied the tiles to a nginx webserver. This server I connected as XYZ in QGIS 3.10.

• The tiles are not at the correct geographic location.
• The order/arrangement of the displayed tiles is incorrect.
• QGIS crashes.

The input virtual rasters are in EPSG3857. The following GDAL command has been used:
python3 -m gdal2tiles -p mercator -z 8 -w none -r average -s EPSG:3857 -a 0.0 C:/Users/usr/AppData/Local/Temp/processing_e4fd1fe4809945ec86e3d5caede62eaa/f7ff49e364cc4f3bb55dc2a7d5fae023/OUTPUT.tif X:2_GIS901_QGISQGISServertilessmr