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FC_DEBUG=4 build/fc-match/fc-match DejaVu output:

...
Add Rule(kind:0, name: /etc/fonts/conf.d/49-sansserif.conf) [test]
        pattern all family NotEqual "sans-serif"
        pattern all family NotEqual "serif"
        pattern all family NotEqual "monospace"
[edit]
        Edit family AppendLast "sans-serif";
...
Rule Set: /etc/fonts/conf.d/11-lcdfilter-default.conf
Substitute Edit lcdfilter Append lcddefault

Append list before  [marker]
Append list after  1(i)(w)
FcConfigSubstitute editPattern has 6 elts (size 16)
        family: "DejaVu"(s)
        hintstyle: 1(i)(w)
        rgba: 1(i)(w)
        lang: "hu"(w)
        lcdfilter: 1(i)(w)
        prgname: "fc-match"(s)

...
Rule Set: /etc/fonts/conf.d/49-sansserif.conf
FcConfigSubstitute test pattern all family NotEqual "sans-serif"
No match

Bisecting resulted in 13015a0a as first bad commit.