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.
out += '\n';
      }
      out += innerMarkup;
    } else {
      children = toArray(props.children);
    }
    var frame = {
      domNamespace: getChildNamespace(parentNamespace, element.type),
      tag,
      children,
      childIndex: 0,
      context: context,
      footer: footer,
    };
    if (__DEV__) {
      ((frame: any): FrameDev).debugElementStack = [];
    }
    this.stack.push(frame);
    this.previousWasTextNode = false;
    return out;
  }
}
export default ReactDOMServerRenderer;