Thanks! Indeed, that's exactly my issue. But I have a different smartcard.
I'm trying to register in the bug reporting tool, but I don't receive the confirmation e-mail.
I see that in the ticket somebody says that it's not possible to reproduce it. In my case, the issue occurs always, even if the smartcard is not present. I assume that it might be possible to reproduce it just by installing the smartcard software that can be downloaded from here (first link): https://www.sede.fnmt.gob.es/en/descargas/descarga-software
Unfortunately, I don't have any spare computer to test if it's reproducible in that way. Perhaps it might also be needed to have a smartcard reader.