![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  
if (traceUpdatesEnabled) {
      const elementType = getElementTypeForFiber(nextFiber);
      if (traceNearestHostComponentUpdate) {
         I
        if (elementType === ElementTypeHostComponent) {
          traceUpdatesForNodes.add(nextFiber.stateNode);
          traceNearestHostComponentUpdate = false;
        }
      } else {
        if (
          elementType === ElementTypeFunction ||
          elementType === ElementTypeClass ||
          elementType === ElementTypeContext ||
          elementType === ElementTypeMemo ||
          elementType === ElementTypeForwardRef
        ) {
           O
          traceNearestHostComponentUpdate = didFiberRender(
            prevFiber,
            nextFiber,
          );
        }
      }
    }
    if (
      mostRecentlyInspectedElement !== null &&
      mostRecentlyInspectedElement.id === id &&
      didFiberRender(prevFiber, nextFiber)
    ) {
       I