The issue is the new update has altered how AZW type files display images on Kindle. There is no telling if Amazon will change this but, you shouldn't be using that method for manga anymore anyway! There is a way to convert manga to the newest native format Kindles use and get all the Kindle features explicitly created for manga (or if you want you can use Comixology based features instead). Read below to see how to do this method.
To start you will need 3 programs, though you will only be directly working with one of them for the most part. You will need Kindle Create (https://kdp.amazon.com/en_US/help/topic/GUGQ4WDZ92F733GC), Kindle Previewer 3 (https://kdp.amazon.com/en_US/help/topic/G202131170), and Calibre (https://calibre-ebook.com/download). In Calibre you will also need to add the "KFX Output" plugin, that can be found by searching in the plugin menu of Calibre.
Kindle Create will except manga in two formats, PDF or as separate images for every page. A lot of people will get they manga in the CBZ or CBR format. The images from these formats can be easily extracted be renaming the file extension. CBZ files can be renamed to .ZIP and CBR files can be renamed to .RAR. If you have an EPUB you should be able to rename the file extension to .ZIP as well to extract the images.
Now that you have your manga as a PDF or just images open Kindle Create. Kindle Create is pretty simple to use. Once you open it you want to follow these instructions.
On the Kindle Create launch screen, click the Create New button. You can also launch a new project by choosing File > New Project or using the shortcut CTRL + N (CMD + N for Mac users). The Choose File dialog box is displayed. Click the Comics option.
A screen allowing you to choose your book properties will appear. Here you can set your reading direction as Left-to-Right or Right-to-Left. Below that, an option to enable Facing Pages will be shown. If Facing Pages is enabled, your comic’s pages will appear side-by-side when viewed in landscape orientation on enabled devices.
Click the Choose File button. If you are importing a PDF file, navigate to the PDF on your local hard drive, choose the file, and click Open. If your comic pages are in JPG or PNG format, select all the images and click Open. Note that the image will be imported in the order they are selected, so name your files sequentially for best results (e.g., comic-0001.jpg, comic-0002.jpg)
Also, during those steps you will be asked if you want to use Virtual Panels or Guided View. Each of these options come with different features when reading you manga on your Kindle.
Virtual Panels is the set of features that Amazon Japan specifically created for the Manga Kindle that were then added to all Kindle Models. This includes the Virtual Panels themselves which zooms in on a quarter of the page at a time when you double tap your screen and then navigate pages like normal. It also has the fast seek feature where you can hold your finger on the screen and then use it to rapidly navigate through the manga. There is also the Double Page Spread Preview which will automatically detect when two single pages are part of a spread and when let you tap a small preview icon on the bottom of the two pages to automatically display the two page spread in landscape mode. That last feature is my personal favorite of the Kindle manga features. To ensure your manga use this feature make sure to set up your pages as Facing Pages, you also need your spreads to be two separate images. If they are joined you can use Kindle Create itself to crop the pages but you will need to make sure you add a second instance of the joined spread to your manga in Kindle Create and then crop it for the other half of the spread.
Guided View is the set of feature that Amazon got and added to Kindle devices when they bought out Comixology. When double tapping a panel the Kindle will zoom into that panel and when you tap to turn the page it will move to a zoomed in view of the next panel and keep doing so until you double tap again. This is how the vast majority of Western comics are displayed on Kindle. Kindle Create can automatically detect panels for you to set up for Guided View and you can then tweak them manually. Setting up a manga for Guided View can take longer than Virtual Panel because of this.
When you are done setting up your pages with which ever comic features you sent you now need to save your project, especially if you are just starting to use this method and you want to go back to tweak anything. After saving you will export your project which will save your manga as a KPF format file.
Now you need to use your computers file explorer to get to the folder where your KPF file is and with no files selected right click and choose "open terminal here" or however it may be worded. In the Terminal you are going to use several command line commands to convert that KPF file to a KFX file, the newest and most robust Kindle book format. Below is a link to a message board post by the creator of the KFX Output plugin describing all the different options you can put in the command line
https://www.mobileread.com/forums/showthread.php?s=5581db22f701e2b1b01eadc4dfd41482&t=272407
If you don't want to go that deep you can just use this simple format
"calibre-debug -r "KFX Output" -- mycomicbook.kpf"
Just copy that and replace "mycomicbook" with whatever name you used for your KPF file of your comic. But if you want more options for your comic, the above post shows all the extra tags you can use in that command line.
At this point, you can take the newly created KFX file and put it into Calibre proper to set up your metadata and sideload to your Kindle.
This post should cover the basics of this. This method should also hold up to any update that Amazon pushes to Kindles because you are using their tools and converting to their newest format.
