I couldn't get logs with journalctl --user-unit gpg-agent (it said No
entries), even when activating debug in gpg-agent.conf. Command gpgconf
--kill gpg-agent reacted like the others: not responding. However, I
managed to make gpg work by stopping all related services (of which I was
not aware, by the way) i.e.
systemctl --user stop gpg-agent{.service,.socket,-ssh.socket,-extra.socket}
After that, gpg-decrypt worked fine.
