This DEV-only field was added in 836331ba5f69f2cc53b273ec073fae116db14302 by @sebmarkbage but it's not being used anymore to my knowledge.
.memoizedState;
        primaryChildFragment.memoizedState =
          prevOffscreenState === null
            ? mountSuspenseOffscreenState(renderLanes)
            : updateSuspenseOffscreenState(prevOffscreenState, renderLanes);
        primaryChildFragment.childLanes = getRemainingWorkInPrimaryTree(
          current,
          renderLanes,
        );
        
        
        workInProgress.memoizedState = SUSPENDED_MARKER;
        return fallbackChildFragment;
      } else {
        
        
        const nextPrimaryChildren = nextProps.children;
        const primaryChildFragment = updateSuspensePrimaryChildren(
          current,
          workInProgress,
          nextPrimaryChildren,
          renderLanes,
        );
        workInProgress.memoizedState = null;
        return primaryChildFragment;
      }
    }
  }
}
function mountSuspensePrimaryChildren(