Costco is my least favorite part of middle age. Although, I do generally like their products and pricing.
For some reason my wife likes taking more time there than other places we shop for food, and I get anxious to get it over with. You can bet most of the times I wander off to get things off our list that she's herself wandered off, and the Costco we go to doesn't have good cell coverage. So I then end up both anxious about spending all day shopping, and annoyed that I can't find my wife.
I am sure I'm not the only one. I try to go alone, or stay in the car this happens so often.
This has nothing to do with Costco. You have described a relationship/communication problem, not a Costco problem.
I figured out that when I push the cart, my wife runs all over and I struggle to keep up and navigate the cart between the crowds and it's an anxiety inducing experience trying to keep up before she turns a corner, then another, never to be seen again.
When she is encumbered with navigating the cart, it's quite easy to stay nearby as all her movements have to be more considered. This also generally restricts her to the same lumbering speed as all the other carts in the store.