When you're running "bleeding edge": Did you adjust the value for muPDF's own store? You might want to set it to a much lower value. It's currently at 64MB, set in line 11 here:
https://github.com/hwhw/kindlepdfvie...reader.lua#L11
That 64MB, then added about 10MB binary size (though cached), plus 5MB tile cache - I can see trouble for the DX with its 128MB... My suggestion is to set that muPDF cache down to 32MB.