Hi, congrats on your new nook, i posted the same question when i got my nook, here is the thread with the replies:
https://www.mobileread.com/forums/sho...d.php?t=180602
I came to the conclusion it's because of the fast refresh and because it only does a hard refresh every 6 pages. I rooted it and read with cool reader for a while, where i could set it to refresh every page-turn, but page turning became much slower as a consequence. I ended up going back to the default reader because i really like the layout of the books and the fonts, and even came to enjoy that fuzzy, ragged look of letters because it makes it resembles the printed book more.