I had the same error time ago and it was generated by a component which was using ref tag, and there was some manual manipulation.
A good practice to see these kind of errors is drawing your app flow and see when your are calling setState.
Another thing I would change if I were you is componentDidMount instead of componentWillMount to check some data. Take into account fb deprecated this functionality.
This lifecycle was previously named componentWillMount. That name will continue to work until version 17. Use the rename-unsafe-lifecycles codemod to automatically update your components.
Reactjs component documentation