![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  
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           T
          nextChild = nextChild.sibling;
           A
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          if (!shouldResetChildren && prevChildAtSameIndex !== null) {
            prevChildAtSameIndex = prevChildAtSameIndex.sibling;
          }
        }
         I
        if (prevChildAtSameIndex !== null) {
          shouldResetChildren = true;
        }
      } else {
        if (traceUpdatesEnabled) {
           I
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          if (traceNearestHostComponentUpdate) {
            const hostFibers = findAllCurrentHostFibers(
              getFiberIDThrows(nextFiber),
            );
            hostFibers.forEach(hostFiber => {
              traceUpdatesForNodes.add(hostFiber.stateNode);
            });
          }
        }
      }
    }
    if (shouldIncludeInTree) {
      const isProfilingSupported = nextFiber.hasOwnProperty('treeBaseDuration');