I see several started authentications in this log file but not the end. Missing “LDAP authentication succeed with principal…” for example.
Anyway the way the authenticator find an already existing user is by searching for an object with “XWiki.LDAPProfileClass” and a field uid
equals to the passed login. Could you edit the user profile with object editor (?editor=object if you are not advanced user) and see if you can find this object.