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.

复现 React 文档和链接的 CodeSandbox 中的 SuspenseList 示例，比较 revealOrder="backwards" 在 500 ms 和 1000 ms trivia 延迟下的表现。首先检查报告中的 experimental React 版本以及示例的 timeout 行为；完成的标准是确定原因，并修正或明确处理较长等待时间下的 backwards 顺序行为。