Professors who grade the same exam dozens or hundreds of times probably experience semantic satiation (explained in the body of the post).

Semantic satiation happens when repeating word or a phrase over and over makes it temporarily lose its meaning. This was first written about in the psychological literature by Titchener, in case you search it online and find that name.

Because word repetition causes defusion (in the Acceptance and Commitment Therapy way), these professors could actually be more cognitively flexible than other people, at least in terms of whatever it is that they're grading.