@JorgeO 

Looking at your nifi-user.log output we see the caused by line as:

Caused by: org.springframework.dao.IncorrectResultSizeDataAccessException: Incorrect result size: expected 1, actual 2

This means that your LDAP/AD returned two results instead of only one.  NiFi then has not idea which of those returns is the correct one it should be using.

So this either an issue within your LDAP/AD or an issue within your current login-identity-providers.xml filters.  But your last shared file looks fine to me.

I would suggest using the ldapsearch command to run a ldap query outside of NiFi to see what returns you get for your admin user (cn=<admin user>)

Hope this helps,

Matt