Ordering of children in a Fragment changes in re-renders

[charlier]

Describe the bug

After updating from 10.16.0 to 10.17.1, when re-rendering, the ordering of children inside a Fragment seems to change.

This sounds suspiciously similar to #4122 - to the point I was just going to add a little "me too" to that issue... But that also seems to happen on older versions of preact & this doesn't rely on preact-compat at all, so I'm not sure if it's unrelated, or has the same underlying root cause.

To Reproduce

Here's a (rather contrived) example with a Fragment (After ~1 second a hook/reducer on a timer will cause a re-render and the content will sit above the header).

https://codesandbox.io/s/dreamy-benji-cm79jk?file=/src/containers/job.js

Either downgrading preact, or Changing the Fragment to just a div as a workaround works flawlessly.