SOLVED: in my ReviewCard component, I was returning one of two pieces of JSX, the second one was a fragment with no key. adding the key removed the recurrent error.

      return (
        <>
          {word}
          {!isLastWord && ' '}
        </>
      );

to

return (
        <React.Fragment key={index}>
          {word}
          {!isLastWord && ' '}
        </React.Fragment>
      );