![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  
}
      const hostFibers = findAllCurrentHostFibers(id);
      return hostFibers.map(hostFiber => hostFiber.stateNode).filter(Boolean);
    } catch (err) {
       T
      return null;
    }
  }
  function getDisplayNameForFiberID(id) {
    const fiber = idToArbitraryFiberMap.get(id);
    return fiber != null ? getDisplayNameForFiber(((fiber: any): Fiber)) : null;
  }
  function getFiberIDForNative(
    hostInstance,
    findNearestUnfilteredAncestor = false,
  ) {
    let fiber = renderer.findFiberByHostInstance(hostInstance);
    if (fiber != null) {
      if (findNearestUnfilteredAncestor) {
        while (fiber !== null && shouldFilterFiber(fiber)) {
          fiber = fiber.return;
        }
      }
      return getFiberIDThrows(((fiber: any): Fiber));
    }
    return null;
  }
  const MOUNTING = 1;
  const MOUNTED = 2;
  const UNMOUNTED = 3;