pass: texlive-base (2022.20220605-1) unstable; urgency=low
fail: texlive-base (2022.20220923-2) unstable; urgency=medium
It should be possible to look at the differences between those (and
maybe the related packages such as texlive-latex-base) to find further
clues. I'm going to start on that fairly soon.
Ok, it turns out that the problem was a compatibility-break between v2
and v3 of the base doc.sty file. Fortunately the texlive-latex-base
package ships the previous (v2, feynmf-compatible) version of that
file along with v3.