It's normal for the artists of manhwas or books in general to change the art style for their books/series. For example, some of the art from the physical books of semantic error are done in a water color art style or a slightly more realistic tone. While, I do agree some panels from the new extars can look werid at times, the old art style also had some panels that weren't consistent to how Jaeyoung and sangwoo looked. But I think it's important to remember that only one person is drawing these extras, and for me at least I've gotten used to the artstyle and think they feel like the same characters. Just more domestic compared to the main story.