Using revealOrder="backwards" in SuspenseList only works for very short wait times

I realize that this is still experimental, but I figured it would still be good to report bugs. If not, feel free to close this issue.

I was playing around with the examples in https://reactjs.org/docs/concurrent-mode-patterns.html#suspenselist and noticed that revealOrder="backwards" didn't seem to work. The trivia items never appear before the posts. After fiddling around with the example in https://codesandbox.io/s/black-wind-byilt i noticed that it works if the timeout is set around 500 ms or below for the trivia items. But if you set it to for example 1000 ms, it will instead wait until both trivia and posts are available.

revealOrder="forwards" seems to work regardless of how long the timeout is.

I tried changing React version to the latest experimental version (0.0.0-experimental-c76e4dbbc-20210722), but it did not seem to make a difference.

Reproduce the SuspenseList example from the React documentation and the linked CodeSandbox, comparing revealOrder="backwards" with 500 ms and 1000 ms trivia delays. Start by checking the reported experimental React version and the example's timeout behavior; done means the cause is identified and the backwards-order behavior is corrected or clearly addressed for longer waits.