After installing Windows updates on Mar. 23, showing the Notebook for an open book in Kindle for PC produces an empty, white pane. It's not simply that my bookmarks and notes are absent, but rather ABSOLUTELY NOTHING is displayed within the Notebook pane.
I narrowed the issue down to either the February 2019 or March 2019 set of Windows updates. The Notebook pane worked as expected after I last installed Windows updates on Feb. 2 (before the February updates were released), and first failed after I installed Windows updates on Mar. 23 (after the March updates were released). Using a publicly-available Windows 8.1 virtual machine, I can reproduce this problem every time (see below). I'm not sure if this is a Microsoft or an Amazon issue, but I'm reporting it here nonetheless.
Import the "IE11 on Win81 (x86)" virtual machine available from Microsoft into your hypervisor of choice and start the virtual machine.
Disable automatic Windows updates to preserve the initial state of the virtual machine (at the time of writing, the above image last had updates applied on Jan. 10, 2018).
Install Kindle for PC and register.
Open a book and show the Notebook. Observe that the Notebook appears as expected, including any bookmarks and notes (see attached before-installing-updates screenshot).
Install the latest Windows updates (at the time of writing, April 2019) and restart.
Start Kindle for PC.
Open a book and show the Notebook.
The Notebook should appear as in step (4).
The Notebook appears as an empty, white pane (see attached after-installing-updates screenshot).
I do not experience this problem on a Windows 7 x64 machine with the latest (April 2019) Windows updates. I did not test Windows 10.
Thanks for forwarding to the dev team! That was my hope when I posted this.
And sorry for not mentioning workarounds... As you pointed out, I can still view my notes and highlights using the cloud reader--as well as the mobile app and my e-reader. It's only on Kindle for PC that I'm experiencing this problem.
I have the same problem and thanks for figuring out it's a problem with Kindle for PC on Windows 8.1. Was a real shocker after getting several hundred pages into a non-fiction book and all highlights and notes gone on the Notebook page.
Since the highlights are still there on my book pages, any idea if the data is there somewhere, but not showing?
You can try a manual Sync from your Kindle for PC app by clicking the Sync icon (two arrows in a circle). You can also enable Whispersync but keep in mind, if you made any notes, highlights, and bookmarks while Whispersync for Books was turned off on your Kindle reading app, you may no longer be able to access them after you turn on Whispersync for Books. Go to the Home screen, select the Menu button or icon, and then select Settings.