Issue with raster stacking

I tried raster stacking using the below code.I tried to read pixel values at a particular coordinate and few values are coming as zero where as when I tried reading the value before stacking there is some pixel value at that particular coordinate. I don’t understand why my raster stacking is causing the issue.

from rasterio import plot
import os
import earthpy.spatial as es

    def image_stack(path, dest_file):
        band_fnames = os.listdir(path)
        band_paths = [path + fname for fname in band_fnames]
        arr, arr_meta = es.stack(band_paths, dest_file)
        return len(band_fnames)