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.
render() {
            return [null, [<Y key="1" />], false];
          }
        }
        function Y() {
          return [<Z key="1" />, ['c']];
        }
        function Z() {
          return null;
        }
        const e = await render(
          <div>
            {[['a'], 'b']}
            <div>
              <X key="1" />
              d
            </div>
            e
          </div>,
        );
        if (
          render === serverRender ||
          render === clientRenderOnServerString ||
          render === streamRender