根据另一个吧友提供的信息:This issue appears to stem from how Kindle software manages eBook metadata. Amazon’s system checks each book’s metadata (like ASIN or ISBN) and matches it to the user’s Amazon Kindle account. If the information in a sideloaded book doesn’t match Amazon’s records and the Kindle has been offline for more than three weeks, the device may flag these files and delete them when it reconnects to Wi-Fi. 这倒是能跟我的情况对得上。