[Samba] Windows login problem to a Samba AD DC

[tizo]

I have a pristine Samba AD DC installed (Samba 4.15 in Rocky Linux 8.5). I
have joined a Windows 10 client without any problems. After restarting, I
try to login with a test user (the only user aside from the administrator),
and it keeps saying "Username or password is incorrect" (maybe this is not
the exact translation, as the language is Spanish). Moreover, I am almost
sure that the password is the right one, as I have tested it with kinit in
the Samba AD DC server. I have also tested with the administrator user with
the same results. It seems to me that Windows doesn't even try to contact
Samba AD DC, as the message is displayed very fast (and no useful
information is logged in Samba AD DC).

So, before entering in more technical details, is there a way to debug the
problem from the Windows client?. I don't really know where to look for
related logs.

JFTR: in previous tests, with another Samba AD DC server but installed in
the same way and with the same versions, I had the same issue with a
Windows 7 client, and a Windows 10 client. The strange thing is that, the
very first time that I joined the Windows 7 client it works, but only for
that day.

Any help is appreciated. Thanks very much.