Yeah they definitely fluctuate, which is kind of why USNews rankings for med school are a little goofy to be honest. I think MCW was 47 last year (not even sure what it is now) but like 53rd when I applied. I know my M1 year the Family Med Dept was ranked 10th in the country by USNews and then wasn't ranked the next year. I think any ranking methodology that allows for that it a little suspect.
I too remember being really interested in the USNews rankings when I was applying, but now couldn't care less. I think the fact that USNews keeps adding different lists (Primary Care, Social Justice, etc.) is because no methodology really works for med schools. My advice is to consider 1) COA, 2) how much you "liked" the school on interview day and 3) location (is it by family, etc.). Those are the things I care about now.