Using KDP for full bleed children's book

Hi guys. Has anyone had any success with this? I have had four proofs with trim errors (i.e. white lines at the top, bottom or side edges of page), all refunded. At least six chats with poorly trained staff, all reading from an answer book, and they all gave contradictory advice as to the changes I needed to make. When I finally got the green light to publish, I ordered an author copy, which arrived with white lines on the side edges of some of my pages. On a full bleed book with colour right up to the edge of the page, this is really noticeable.

On their manufacturing issues page, KDP themselves mention that they have a trim variance of up to 3.3mm and that's just how it is when publishing through them. Does that mean that they simply aren't capable of printing full bleed books with consistent and professional quality? Is there always going to be a chance that paying customers are going to receive a book with visible white trim? Because if they do, they'll be reviewing the book poorly, not the people who published it.

What do people think? I'd love some input on this. Thanks in advance.