Based on the error message df_row['building_label_path'], 0) is a np.float64 while cv2.imread expects a str as seen here:
cv2.imread(np.float64(2.))
> TypeError: Can't convert object of type 'numpy.float64' to 'str' for 'filename'

cv2.imread(str(np.float64(2.))) # works but returns None as it's an invalid file name

Make sure to pass a valid path as a string to imread.