Understand there are several types of editors. Just because you hire one, doesn’t mean they’ll do the job you expect, especially if you don’t understand there are different types. They may do a great job within their realm, yet miss other problems. I can’t tell you how many problems I’ve found in books where the author supposedly hired an “editor.”
Here’s the basic run-down: Proofreaders look for typos. Copy editors look at punctuation and grammar. Line editors look at everything. Content editors look at plot & characterizations. If this is news to you, then I suggest you read this great article that gives more detail.