Here’s another gripe on the “doesn’t get 5-stars” list, though I haven’t seen this one quite as often. This one is when the main character is forgotten. I’ve seen stories that started out with one person and then s/he disappeared at some point and someone else took over.
Huh? Whose story is it? Even the first chapter should start out with the main character, which is sometimes violated, and may cause the confusion in the first place. If someone off-stage is key, use a prologue.
I saw this happen in one book recently where this transition would have been the perfect place to end it and segue into the sequel. However, doing it halfway through the book definitely didn’t work for me. You just get connected with a character and then he disappears? WTF!