`componentWillMount` warnings although no explicitly used

You're getting this warning because componentWillMount is deprecated in newer React versions. If you're not using componentWillMount anywhere then one of your libraries is and it needs to be updated.

If it makes you feel better, your production build will not show these warnings in the console.

If you are unable to update libraries for whatever reason, you can try suppressing these errors in the console by putting something like console.warn = () => {} At the top of your App component but I wouldn't recommend this since then you won't be able to use console.warn later in your code. Best to just accept them as an annoyance until you're able to update your library.