The really subtle footgun that I see is unexpected state preservation. This is where the component isn't designed to be "reused" for completely different props. This is because the state has something about the props and will end up unhappy if they change.

Some common warning signs are generic parameters for components and using a prop as the default value for a state hook. But neither of these are a reliable indicator of a problem.

These bugs also often lie hidden for a long time because They can be hard to trigger because you need the same structure of components with a generic property changed. But when they bite they seem like impossible errors.

I've wondered if React could add a useStateKey([deps]) hook that would allow forcing a state reset if the given values change. This would work similar to a key attribute but be controllable by the code inside the component.