Troubleshooting Kindle Touch - No books on home screen: Bug, or Amazon?

[viragored]

TLDR: Kindle Touch, connects to wifi for first time in years, all books vanish from the home screen. Any tips, clues, suggestions?
Full story below...

I've had a Kindle Touch for about 10 years. Early on I applied the Jailbreak and Cover Screen hack (exactly how is now lost in the mists of time). The Kindle worked fine up to a couple of weeks ago - when I connected to wifi for the first time since the early days.

Now that Amazon will only send books to the Kindle and not download/USB transfer, I wanted to load the dozen or so books I'd bought recently. I used the Amazon 'Devices and Content' web page to select them. They seemed to download successfully - but the home screen showed no books. Both Calibre and Windows explorer showed that the 100 or so books previously on the Kindle were still there, in the author-based folder structure. The books just downloaded were in the Kindle, but as single files in the root folder and not imported/indexed into the folders.

I've tried all combinations of the filters - Device/Cloud, All Items/Books, Latest/Author/Title. And still the number of items is shown as 0.

The various attempts I've made to get things working again include:

• Reboot the Kindle, both from the home screen/Settings menu and from long-press the power button (several times)
• Reload the firmware (which was and still is 5.3.7.3, the latest supported for Kindle Touch)
• Reset the Kindle (twice) from the home screen/Settings menu so device is "factory fresh" with no Jailbreak, etc.

After the first reset, I loaded some books onto the Kindle from Calibre. They appeared on the home screen, as expected. And then they disappeared from the home screen again after I'd finished one book and gone back to the home screen. Then I connected to the wifi, intending to download again the books that had been removed by the reset - and the Kindle started loading empty collections, over 40 of them, that did appear on the home page. I turned off the wifi, deleted the collections and still had no books on the home page.

After the second reset I again loaded some books from Calibre and started reading another book. All was going well, all the books I'd loaded were still showing on the home page after some days. To get more books from Amazon I tapped the Cloud option on the home page, which popped up a list of almost 1000 books (presumably all I've got in my Amazon account) - with the wifi off. Then I connected the wifi, selected one book which downloaded successfully and opened for reading.
And that's when all the books again disappeared from the home screen.

The books are there because a home screen search can find them, and then take me to the book.

So I'm wondering if this is a bug linked to wifi connection, there's an issue with the amount of processing the software needs to do after a reset, or the Kindle is being sabotaged by Amazon because of books coming in from Calibre.
Anyone got any suggestions?