The attached PDF contains subset fonts not recognised as subset:
$ pdffonts x.pdf
name type encoding emb sub uni object ID
------------------------------------ ----------------- ---------------- --- --- --- ---------
Gentium CID TrueType Identity-H yes no yes 7 0
Gentium-Italic CID TrueType Identity-H yes no yes 8 0
MScore CID TrueType Identity-H yes no yes 9 0
FreeSerif CID TrueType Identity-H yes no yes 10 0
FreeSerifBold CID TrueType Identity-H yes no yes 11 0
Inconsolatazi4varl_qu-Regular CID TrueType Identity-H yes no yes 12 0
NotoSansSymbols-Regular CID TrueType Identity-H yes no yes 13 0
(same output for stable and unstable)
Qt5, which generated this PDF, has subset them, but in a devious way:
the top-level fonts are type0 collections, and their descendant fonts
only are subset.
ps2pdf fixes this up, of course, its output then is properly recognised
as subset, but not the original Qt5 output