Doitsu,
I replaced the font, used your azw3 file, but got the same result.
In the font-hack folder of the kindle, there is a text file named info.txt, which reads:
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$Id: info.txt 8953 2012-11-15 23:23:21Z NiLuJe $
Hello! If you're wondering what all this weird stuff on your Kindle is,
I'm a fonts hack! There's a good chance that I came from here:
https://www.mobileread.com/forums/showthread.php?t=88004
I'm at version 5.6.N, so, if you wish to uninstall me, you'll at least need
the uninstaller from that version.
-- NiLuJe
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As I got this k4nt as it is, I have no idea if the font-hack it has is the most up-to-date version or not.
(I used the same mobi and your azw3 file on Kindle app on Android and iOS. Interestingly, the Android app works correctly while the iOS app is not.)