@guy_rouillier Hi there.
Ubuntu Discourse moderator here: we are not aware of any current issues like this.
I checked your user profile and everything seems fine.
I would, firstly, check the console as @Moin suggested but also try clearing cache and cookies for the site then hard reset with Shift or Ctrl + F5 and then try logging in again.
I will keep an eye on this topic and also over at Ubuntu Discourse.
If you do manage to log in, please ping me a PM to let me know (@rubi1200)
Hopefully this gets resolved soon.