React version: 0.0.0-f77c7b9d7
Browser: Chrome Version 84.0.4147.105 (Official Build) (64-bit)
OS: Ubuntu 18.04.4 LTS

## Steps To Reproduce

1. move mouse over button

Link to code example:

https://codesandbox.io/s/mouseenter-in-reactnext-ibld3?file=/src/Demo.js

## The current behavior

`onMouseEnter` fires twice (sometimes it doesn't).

![video capture of repro steps](https://i.ibb.co/XzdQF68/react-next-mouseenter-twice.gif)

## The expected behavior

It fires only once. Same repro with `react@16.13.1`: https://codesandbox.io/s/mouseenter-in-react16131-9sr7b?file=/src/Demo.js

dispatchQueue: DispatchQueue,
  domEventName: DOMEventName,
  targetInst: null | Fiber,
  nativeEvent: AnyNativeEvent,
  nativeEventTarget: null | EventTarget,
  eventSystemFlags: EventSystemFlags,
  targetContainer: EventTarget,
) {
  const isOverEvent =
    domEventName === 'mouseover' || domEventName === 'pointerover';
  const isOutEvent =
    domEventName === 'mouseout' || domEventName === 'pointerout';
  if (isOverEvent && (eventSystemFlags & IS_REPLAYED) === 0) {
    const related =
      (nativeEvent: any).relatedTarget || (nativeEvent: any).fromElement;
    if (related) {
      
      
      
      
      const inst = getClosestInstanceFromNode(related);