![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  
child = child.sibling;
        }
         W
         w
        throw Error('Unable to find node on an unmounted component.');
      }
      if (a.return !== b.return) {
         T
         f
         b
         s
        a = parentA;
        b = parentB;
      } else {
         T
         d
         w
        
         S
        let didFindChild = false;
        let child = parentA.child;
        while (child) {
          if (child === a) {
            didFindChild = true;
            a = parentA;
            b = parentB;
            break;
          }
          if (child === b) {
            didFindChild = true;