building notes fails on producing diff pdf

It happened for this job in Lowdin project:

fatal: Path 'notes/notes.tex' exists on disk, but not in 'f0dbad2df9cec3895860bf91ca9c43de39d262e3'.

It is surprising for me why as this file shouldn't be present in last good build and therefore conditional block

    -     if [ "$LAST_GOOD_SHA" ] && [ "$DIFF" ]; then
    -       git show $LAST_GOOD_SHA:$CWD/$tex > old_$tex
    -       latexdiff old_$tex $tex > diff_$tex
    -       rm old_$tex
    -       latexmk -pdf diff_$tex
    -     fi

should not be executed.

It's the first time I saw something like this so maybe just something weird happened in this project. I will report here if I see the issue again.