PW2: Latest .mobi books loaded through USB are not visible on a Home screen

[Yury]

A few latest .mobi books that were created/converted by Calibre and loaded with Windows File Manager through USB cable are not visible on a Home screen of my PW2.
I already have about 200 books on this device and most of them were created/converted by Calibre and loaded through USB interface over the last several years.

Troubleshooting:
1) I copied a couple of these books to my Kindle K4 and they are visible on a Home screen of that device.
So I assume that this is sufficient conformation that these books are not broken.

2) I deleted content of a "System/Search Indexes" folder of Kindle PW2
- disconnected from PC
- connected to PC
- Index started getting rebuilt: .lg and .db files reappeared - .lg = 1 KB; .db = 40 KB
- disconnected from PC
- connected to external power source
- closed the lid
- waited until indexing has finished (searched for "." and "Text in Books (0)" menu was greyed out)
- these books have not appeared on a Home screen

I would appreciate an advice on how to access these books.
I have quite a few books in partially read state and would like to avoid "Reset" command.

Note: It was the first attempt to load books that were created/converted on a new laptop with a new version of Calibre. I am not sure whether this is important because the same books were successfully loaded on Kindle K4.
All other steps were the same that worked OK for me before.

[Sirtel]

Convert to azw3, not mobi.

[Yury]

Originally Posted by Sirtel

Convert to azw3, not mobi.

Why to convert to .azw3?
What's wrong with these 3 .mobi files as compared to previous 150 .mobi files that were loaded OK?

Note: I converted these 3 books to .azw3 and was able to see them on my Kindle.