Hi again,
I tried to create an article with the same query loop as on my front page, and it works (https://redero.fr/?p=134).
Somehow it seems that the bug only affects the first query loop on the main page, because if I call a second query loop on front page, it appears bug-free.
(So as a really shameless quick fix, I called a mock query loop before the real one, and made sure the content returned by the mock query was empty.)