I went through this before and am now facing it again. ALL 1000+ images for each album are numerically named. I uploaded about 170 to an album and manually sorted them. VERY time consuming and frustrating as the images are quite large (Sort Album) view and only a few show on screen at any one time.
I then needed to add more. Tried FTP and they appeared BEFORE of the first image of the album. So, ended up having to sort one-by-one. Tried ZP upload. Same thing. Tried again FTP and not sure what happened but EVERY image, now over 180, is unsorted!!!
Of note, I cannot tell which image is which as I do not get the pointer changing and there's no image names showing when hover over (must be a Mac thing). So, sorting is excrutiating