thumbpdf not generating png thumbnails

I have tried to use thumbpdf to try and generate thumbnails, working directly on the pdf file, like this:

thumbpdf cv.pdf

This has worked the first time, and produced the corresponding cv-xxx.png files, as well as a cv.tpt file. However, it hasn’t worked again (even if the PDF has changed), or in a Github action environment, where it outputs this correctly:

THUMBPDF 3.17, 2018/09/07 - Copyright (c) 1999-2018 by Heiko Oberdiek.
*** make png files / run Ghostscript ***
!!! Warning: MediaBox not found, using default resolution: 9 DPI
Processing pages 1 through 4.
[1] [2] [3] [4]
*** make `thumbpdf.pdf' / run pdfTeX ***
*** parse `thumbpdf.pdf' ***
*** write `cv.tpt' (pdfTeX thumbnail data) ***
*** clear temp files ***
*** ready. ***
citations-year.png
cv.png
paper-citations-year-log.png
paper-citations-year-nolog.png
mv: cannot stat 'cv-0.png': No such file or directory
Error: Process completed with exit code 1.

But it’s not producing any .png file at all. I have seen there’s an option --make-png, but it’s supposed to be activated by default, so that should not be it… Any idea?