### Describe what you were doing when the bug occurred:
1. I did profiling on a list, that gets updated on each pagination api call.
2. Once the profiling was done, I moved around in the Profiler to view the Flamegraph
3. Moving to second capture, the Profiler crashed.


**DevTools version**: 4.6.0-6cceaeb67

```
Component stack: in ec
    in div
    in div
    in div
    in So
    in Unknown
    in n
    in Unknown
    in div
    in div
    in rl
    in Ze
    in fn
    in Ga
    in _s
```
function findCurrentFiberUsingSlowPathById(id: number): Fiber | null {
    const fiber = idToFiberMap.get(id);
    if (fiber == null) {
      console.warn(`Could not find Fiber with id "${id}"`);
      return null;
    }
    const alternate = fiber.alternate;
    if (!alternate) {
       If 
      const state = isFiberMountedImpl(fiber);
      if (state === UNMOUNTED) {
        throw Error('Unable to find node on an unmounted component.');
      }
      if (state === MOUNTING) {
        return null;
      }
      return fiber;
    }
     If we have two possible branches, we'll walk backwards up to the root
     to see what path the root points to. On the way we may hit one of the
     special cases and we'll deal with them.
    let a: Fiber = fiber;
    let b: Fiber = alternate;
    while (true) {
      const parentA = a.return;
      if (parentA === null) {
         We'
        break;
      }
      const parentB = parentA.alternate;