这是在 Windows 10 更新中，然后就突然出现这个问题。
- 重新从“文件”选项卡 -> “打开”项 -> “从 OneDrive 打开”，找到该笔记本，重新打开，同步下来就好。
来自 OneNote 小组产品经理的解释
I'm a Product Manager on the OneNote team responsible for OneNote's sync and storage infrastructure. As many of you noticed yesterday, some OneNote users opening the app were shocked to see that OneNote seemed to have deleted all their notes!
Fortunately, that wasn't the case. The OneDrive team made a change to their service which started serving improperly formatted notebook URLs to OneNote clients. OneNote didn't know what to do with URLs which had a "" character in them, as many curious users discovered for themselves. When our app attempted to search the location for the sections it thought were in the notebook, it couldn't find any and proceeded to hide sections that were already downloaded from the user as it thought they didn't exist.
Thankfully, the OneDrive team quickly fixed this issue and we're thinking about updating our modern clients to fail more gracefully when given URLs like the ones returned by OneDrive.
On behalf of the OneNote team, I want to say we're sorry for any inconvenience or stress we might've caused! Thanks for sticking with us and being fans of the product we're building.
Also - huge thanks to /u/redarcher09 and /u/rannelvis whose diagnoses tipped us off to what was causing this problem. Without this feedback, there'd be a good chance of this issue still not being resolved.
Thanks again for the feedback and unprompted troubleshooting info. While the Product team might not always be super active on this subreddit, rest assured we're big time lurkers and really value your input. We have the best users! :)