Hi Kurt,
Are you talking about the line of CJK text after "=head2", and specifically the 5th character from the right? I looked at it on my Win10 system with Adobe Acrobat Reader DC, FireFox, Chrome, and Edge; and in all cases all four pages showed this character. In other words, it was all there.
So, I'm confused. The glyph is definitely there in the PDF. Are you saying that some font versions are missing this character? Are these problems fixed by upgrading the fonts (in which case this is not a PDF::Builder problem, but a local problem)? Or is there a CMAP problem somewhere (glyph-to-Unicode point mapping)? Remember that usually CJK fonts are not embedded in PDFs (I don't know why), and local font copies are used. Using ttfont() instead, some CJK fonts will embed, and some will even subset (just the glyphs used).
Phil