(Fiction) Reading is an experience. It’s a momentary journey into another world, even if the world mirrors our own. Sometimes, that’s even true in nonfiction.
Sometimes, a character is “flat,” two-dimensional, as a form of satire or commentary. Maybe the backstory would make you empathize with a character, but the character is still evil. Maybe the focus of the story is “what,” not “who.”
My thought is: recognize it. Own it. And then decide if the story is okay with that. Maybe it is, and your work (in this regard) is done. Maybe not. Maybe your character just does not make sense like that. Maybe the story is too scattered without focusing that character a bit.
Editing requires me to step back from being a writer and become a reader. Because that’s who I’m trying to entertain. Not myself and not the agent.