React playground fails with TypeError and React Invariant Violation

[kleest]

React playground fails with the following two erros:

react-onsenui.min.js:1 Uncaught TypeError: Cannot read properties of undefined (reading 'string')
    at react-onsenui.min.js:1:14787
    at react-onsenui.min.js:1:4243
    at react-onsenui.min.js:1:4357

and

react-dom.min.js:15 Uncaught Invariant Violation: Minified React error #130; visit http://facebook.github.io/react/docs/error-decoder.html?invariant=130&args[]=undefined&args[]=%20Check%20the%20render%20method%20of%20%60MyPage%60. for the full message or use the non-minified dev environment for full errors and additional helpful warnings.
    at r (https://cdnjs.cloudflare.com/ajax/libs/react/15.4.2/react-dom.min.js:15:17790)
    at p.i [as _instantiateReactComponent] (https://cdnjs.cloudflare.com/ajax/libs/react/15.4.2/react-dom.min.js:15:15991)
    at p.performInitialMount (https://cdnjs.cloudflare.com/ajax/libs/react/15.4.2/react-dom.min.js:13:6780)
    at p.mountComponent (https://cdnjs.cloudflare.com/ajax/libs/react/15.4.2/react-dom.min.js:13:5742)
    at Object.mountComponent (https://cdnjs.cloudflare.com/ajax/libs/react/15.4.2/react-dom.min.js:14:18733)
    at p.performInitialMount (https://cdnjs.cloudflare.com/ajax/libs/react/15.4.2/react-dom.min.js:13:6856)
    at p.mountComponent (https://cdnjs.cloudflare.com/ajax/libs/react/15.4.2/react-dom.min.js:13:5742)
    at Object.mountComponent (https://cdnjs.cloudflare.com/ajax/libs/react/15.4.2/react-dom.min.js:14:18733)
    at a (https://cdnjs.cloudflare.com/ajax/libs/react/15.4.2/react-dom.min.js:14:10575)
    at r.perform (https://cdnjs.cloudflare.com/ajax/libs/react/15.4.2/react-dom.min.js:15:8936)

These errors occur regardless of the selected code example.