I definitely experience this all the time!! It seems like particular authors or writing styles are more difficult to understand. My professors literally wrote the textbook for some of my courses...and they're terrible at it. While the books were accurate their writing styles are very strange and organized illogically. I literally spent days reading a single chapter.

Now a graduate, I spend my days researching books and articles written by authors and publishers that will likely be the easiest for me to read based on reading their past materials....as long as they're reputable and relevant, of course.

After that random ramble; you're not alone!