I took a quick look at your book but did not see where you used an @fontface to link the font in the fonts directory to your ebook. I haven't tried that in a while but did remember having to do this a few years back.
I tried this and epub had not issue while kepub did require publisher default to show the alternate font. I've attached the epub with the @fontface bits and a couple of screenshots (1st is the epub, 2nd is the kepub).
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