This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
} else {
      deletions.push(currentFallbackChildFragment);
    }
  }
  workInProgress.child = primaryChildFragment;
  return primaryChildFragment;
}
function updateSuspenseFallbackChildren(
  current,
  workInProgress,
  primaryChildren,
  fallbackChildren,
  renderLanes,
) {
  const mode = workInProgress.mode;
  const currentPrimaryChildFragment: Fiber = (current.child: any);
  const currentFallbackChildFragment: Fiber | null =
    currentPrimaryChildFragment.sibling;
  const primaryChildProps: OffscreenProps = {
    mode: 'hidden',
    children: primaryChildren,
  };
  let primaryChildFragment;
  if (
    
    
    (mode & ConcurrentMode) === NoMode &&