When opening my raster with QGIS, I can see the Pixel Size of my raster as:

0.0008333333299974727193,-0.000833333330020215703

When I read he same raster with rasterio, I get pixel size values with a lower precision and I guess this causes some problems when calculating new affines for another extent

0.0008333333299974727 0.0008333333300202157

I have tries to pass the decimal_precision=X when opening my raster with rasterio, but this has no effect. I guess this is a general float problem on my system. My suggestion therefore would be to use python Decimals or any other type representing real floats.