Follow up from https://github.com/facebook/react/pull/11616.

Here's one I found. These two invariants:

https://github.com/facebook/react/blob/7e7127387ba64f57299eaff8656542cea6fb3a2d/packages/react-reconciler/src/ReactFiberClassComponent.js#L330-L343

are in a function that's behind a DEV block:

https://github.com/facebook/react/blob/7e7127387ba64f57299eaff8656542cea6fb3a2d/packages/react-reconciler/src/ReactFiberClassComponent.js#L447-L449

I don't think this is intentional, but need to verify.

There may be more. I'll use this issue to track while https://github.com/facebook/react/pull/11616 preserves existing behavior.
let Header = props => {
        return <p>header</p>;
      };
      let Footer = props => {
        return (
          <React.Fragment>
            <h2>footer</h2>
            <h3>about</h3>
          </React.Fragment>
        );
      };
      let e = await render(
        <React.Fragment>
          <div>text1</div>
          <span>text2</span>
          <Header />
          <Footer />
        </React.Fragment>,
      );
      let parent = e.parentNode;
      expect(parent.childNodes[0].tagName).toBe('DIV');
      expect(parent.childNodes[1].tagName).toBe('SPAN');
      expect(parent.childNodes[2].tagName).toBe('P');
      expect(parent.childNodes[3].tagName).toBe('H2');
      expect(parent.childNodes[4].tagName).toBe('H3');
    });
    itRenders('a nested fragment', async render => {
      let e = await render(
        <React.Fragment>
          <React.Fragment>