not sure how the file size being small is still causing this, but i know that when you do these processes sims locks the photo files as in use. it doesn't just use the filename to do the comparison, it's holding the things in memory in a bad way i guess, and then doing some inefficient coding. you may be better off, splitting off say 100 photos, and not filtering the list, this may be easier.

it'll be much easier to break down the number of photos and not filter the year, than the other way around, but i guess vertical groups is not helping you.