Hi, Murillo.
First, regarding the initial issue: I was informed there [was a bug](https://github.com/GluuFederation/oxTrust/issues/789), it will be fixed in 3.1.2
>So, if I want to use two or more LDAPs for user authentication, should I use cache refresh?
If you plan to use authentication against some backend LDAP server (instead of Gluu's own LDAP server), in almost all cases you'll need to use CR at least for initial importing of users from it. It doesn't matter how much servers you'll specify on "Manage authentication", but usually servers' layout there match the one you specify for CR.
>we would directly use LDAP Authentication (without cache refresh)
Gluu requires that for each user that tries to access it an internal cached entry must exist. Even if you delegate the actual authentication to some remote party, like your organization's LDAP server, there still must be a corresponding user entry in Gluu's internal LDAP server, which will store all user's attributes to release them upon request from SPs/RPs. Cache Refresh does exactly this.
Overall, I would suggest to be extremely cautious when you are doing any experiments with authentication settings, as you can lock out yourself from web UI. Please create a vm snapshot, and keep admin web UI session constantly active in a separate browser so you could revert your settings.