Why are my React list items buggy when reordered?

Usually because you mutated the state variable directly instead of using the setter, or mutated an object in place so React did not detect a reference change. Always use the setter and replace objects and arrays with new copies.

Because it creates two sources of truth that can drift apart. When the prop changes, the copied state does not update, causing bugs. Keep one source of truth and let the parent own the value.

You are calling a state setter directly in the render body. Only update state inside event handlers, effects, or callbacks. Calling the setter during render triggers a re-render that calls it again, creating a loop.