![Screenshot 2019-12-16 10 51 05](https://user-images.githubusercontent.com/793565/70934095-fd91ed80-1ff1-11ea-93b5-746e816585ec.png)
There's seems to be circumstances where unmounted DOM/Fibers are kept alive by React DevTools. They're kept alive in `primaryFibers`:
https://github.com/facebook/react/blob/34527063083195558f98108cde10b5d6ad0d6865/packages/react-devtools-shared/src/backend/renderer.js#L772

It seems like a WeakSet would be appropriate and would remove the leak. Otherwise we'd need to understand why recordUnmount isn't called.

CC @bvaughn  
primaryChild,
              shouldIncludeInTree ? fiber : parentFiber,
              true,
              traceNearestHostComponentUpdate,
            );
          }
        }
      } else {
        if (fiber.child !== null) {
          mountFiberRecursively(
            fiber.child,
            shouldIncludeInTree ? fiber : parentFiber,
            true,
            traceNearestHostComponentUpdate,
          );
        }
      }
       W
       I
      updateTrackedPathStateAfterMount(mightSiblingsBeOnTrackedPath);
      fiber = traverseSiblings ? fiber.sibling : null;
    }
  }
   We use this to simulate unmounting for Suspense trees
   when we switch from primary to fallback.
  function unmountFiberChildrenRecursively(fiber: Fiber) {
    if (__DEBUG__) {
      debug('unmountFiberChildrenRecursively()', fiber);
    }
     W