Redmine

I've migrated from a 2.4.2 Redmine server to a new 3.2.1.
Everything is working OK but failing to test LDAPS (LDAP + SSL) connections (LDAP connections without SSL are working OK).
I've tested with different users and different LDAP servers and always get the same result: auth_source form shows an error message: "Unable to connect (hostname X.X.X.X does not match the server certificate)".
I've not found relevant info in production.log file:

Started PATCH "/auth_sources/8" for 172.19.12.124 at 2017-09-25 12:46:16 +0200
Processing by AuthSourcesController#update as HTML
  Parameters: {"utf8"=>"✓", "authenticity_token"=>"Fa1QoVLFef+zngYYwypUipDda1/c0Yh0mqqGmtWThvA0D2zNmqqeDLiGUwN0pwgTWfklBjrZ73G4KpDo/53qTA==", "auth_source"=>{"name"=>"OpenLdap", "host"=>"X.X.X.X", "port"=>"636", "tls"=>"1", "account"=>"uid=xxxxxxx,ou=xxxxxx,dc=xxxxx,dc=xx", "base_dn"=>"ou=xxxxxx,dc=xxxxxx,dc=xx", "filter"=>"", "timeout"=>"", "onthefly_register"=>"0", "attr_login"=>"sAMAccountName", "attr_firstname"=>"", "attr_lastname"=>"", "attr_mail"=>""}, "dummy_password"=>"[FILTERED]", "commit"=>"Save", "id"=>"8"}
  SQL (4.3ms)  UPDATE `tokens` SET `tokens`.`updated_on` = '2017-09-25 12:46:16' WHERE `tokens`.`user_id` = 1 AND `tokens`.`value` = '932b09e00f3e76cd17f3b9b92f4dfacc77b0b3c2' AND `tokens`.`action` = 'session' AND (created_on > '2017-09-24 12:46:16.911570') AND (updated_on > '2017-09-25 00:46:16.911805')
   (0.3ms)  SELECT MAX(`settings`.`updated_on`) FROM `settings`
  User Load (0.3ms)  SELECT  `users`.* FROM `users` WHERE `users`.`type` IN ('User', 'AnonymousUser') AND `users`.`status` = 1 AND `users`.`id` = 1 LIMIT 1
  Current user: admin (id=1)
  AuthSource Load (0.2ms)  SELECT  `auth_sources`.* FROM `auth_sources` WHERE `auth_sources`.`id` = 8 LIMIT 1
   (0.1ms)  BEGIN
  AuthSource Exists (0.3ms)  SELECT  1 AS one FROM `auth_sources` WHERE (`auth_sources`.`name` = BINARY 'OpenLdap' AND `auth_sources`.`id` != 8) LIMIT 1
  SQL (0.2ms)  UPDATE `auth_sources` SET `port` = 636, `tls` = 1 WHERE `auth_sources`.`id` = 8
   (1.2ms)  COMMIT
Redirected to https://<my_server>/auth_sources
Completed 302 Found in 15ms (ActiveRecord: 6.8ms).

I've tested from SSL connections with openssl to LDAP connection with ldapsearch, and it not seems to be anything wrong.
Using the same users credentials and the same server connections (early configured into Redmine), with ldapseach goes everything OK.

Data about my environment:

root@asscc111s:/usr/share/redmine# ruby bin/about

Environment:
  Redmine version                3.2.1.stable
  Ruby version                   2.3.1-p112 (2016-04-26) [x86_64-linux-gnu]
  Rails version                  4.2.6
  Environment                    production
  Database adapter               Mysql2
SCM:
  Git                            2.7.4
  Filesystem
Redmine plugins:
  no plugin installed

root@asscc111s:/usr/share/redmine# mysql -V
mysql Ver 14.14 Distrib 5.7.19, for Linux (x86_64) using EditLine wrapper

Finally, all installed over a Ubuntu Server 16.04.