Could you please upload a bit more from the log? Ideally start capturing before you start reproducing and makd sure it contains response (Completed ...) line for the last query. What is your version of ldap_fluff library?

The output of production.log when I tried edit existed LDAP source (I clicked 'Submit' button 3 times):

2017-10-23 17:32:38 b3990428 [app] [I] Started GET "/auth_source_ldaps/3-EXAMPLE/edit" for 172.16.28.83 at 2017-10-23 17:32:38 +0300
2017-10-23 17:32:38 b3990428 [app] [I] Processing by AuthSourceLdapsController#edit as */*
2017-10-23 17:32:38 b3990428 [app] [I]   Parameters: {"id"=>"3-EXAMPLE"}
2017-10-23 17:32:38 b3990428 [app] [I] Current user: admin (administrator)
2017-10-23 17:32:38 b3990428 [app] [I]   Rendered taxonomies/_loc_org_tabs.html.erb (2.1ms)
2017-10-23 17:32:38 b3990428 [app] [I]   Rendered auth_source_ldaps/_form.html.erb (27.0ms)
2017-10-23 17:32:38 b3990428 [app] [I]   Rendered auth_source_ldaps/edit.html.erb (31.2ms)
2017-10-23 17:32:38 b3990428 [app] [I] Completed 200 OK in 49ms (Views: 34.0ms | ActiveRecord: 4.0ms)
2017-10-23 17:32:41 1fc466f7 [app] [I] Started GET "/notification_recipients" for 172.16.28.83 at 2017-10-23 17:32:41 +0300
2017-10-23 17:32:41 1fc466f7 [app] [I] Processing by NotificationRecipientsController#index as JSON
2017-10-23 17:32:41 1fc466f7 [app] [I] Current user: admin (administrator)
2017-10-23 17:32:41 1fc466f7 [app] [I] Completed 200 OK in 5ms (Views: 0.1ms | ActiveRecord: 0.8ms)
2017-10-23 17:32:45 4498b80a [app] [I] Started PATCH "/auth_source_ldaps/3-EXPAMPLE" for 172.16.28.83 at 2017-10-23 17:32:45 +0300
2017-10-23 17:32:45 4498b80a [app] [I] Processing by AuthSourceLdapsController#update as */*
2017-10-23 17:32:45 4498b80a [app] [I]   Parameters: {"utf8"=>"✓", "authenticity_token"=>"GgES45cnqqLH7yTWKtL086Xgoqw40RCxy72Nl+RTiGtkbw+JwV4KUtvt2Vjl95oI76/4v22BEzn4pEEKcaWipQ==", "auth_source_ldap"=>{"name"=>"example1", "host"=>"example.ru", "tls"=>"0", "port"=>"389", "server_type"=>"active_directory", "account"=>"ad_auth", "base_dn"=>"DC=example,DC=ru", "groups_base"=>"OU=Security Groups,DC=example,DC=ru", "use_netgroups"=>"0", "ldap_filter"=>"memberOf=CN=puppet,OU=Security Groups,DC=example,DC=ru", "onthefly_register"=>"0", "usergroup_sync"=>"1", "attr_login"=>"userPrincipalName", "attr_firstname"=>"givenName", "attr_lastname"=>"sn", "attr_mail"=>"mail", "attr_photo"=>""}, "_ie_support"=>"", "id"=>"3-EXAMPLE"}
2017-10-23 17:32:45 4498b80a [app] [I] Current user: admin (administrator)
2017-10-23 17:32:45 4498b80a [app] [I] Failed to save:
2017-10-23 17:32:45 4498b80a [app] [I]   Rendered taxonomies/_loc_org_tabs.html.erb (0.1ms)
2017-10-23 17:32:45 4498b80a [app] [I]   Rendered auth_source_ldaps/_form.html.erb (15.2ms)
2017-10-23 17:32:45 4498b80a [app] [I]   Rendered auth_source_ldaps/edit.html.erb (15.7ms)
2017-10-23 17:32:45 4498b80a [app] [I] Completed 200 OK in 31ms (Views: 16.3ms | ActiveRecord: 3.8ms)
2017-10-23 17:32:50 c7eee74e [app] [I] Started PATCH "/auth_source_ldaps/3-example1" for 172.16.28.83 at 2017-10-23 17:32:50 +0300
2017-10-23 17:32:50 c7eee74e [app] [I] Processing by AuthSourceLdapsController#update as */*
2017-10-23 17:32:50 c7eee74e [app] [I]   Parameters: {"utf8"=>"✓", "authenticity_token"=>"UcP2WN3jiATBb33PFcxMIjnn3N107LWl1S+Hq1lFLTYvresyi5oo9N1tgEHa6SLZc6iGziG8ti3mNks2zLMH+A==", "auth_source_ldap"=>{"name"=>"example1", "host"=>"example.ru", "tls"=>"0", "port"=>"389", "server_type"=>"active_directory", "account"=>"ad_auth", "account_password"=>"[FILTERED]", "base_dn"=>"DC=example,DC=ru", "groups_base"=>"OU=Security Groups,DC=example,DC=ru", "use_netgroups"=>"0", "ldap_filter"=>"memberOf=CN=puppet,OU=Security Groups,DC=example,DC=ru", "onthefly_register"=>"0", "usergroup_sync"=>"1", "attr_login"=>"userPrincipalName", "attr_firstname"=>"givenName", "attr_lastname"=>"sn", "attr_mail"=>"mail", "attr_photo"=>""}, "_ie_support"=>"", "id"=>"3-example1"}
2017-10-23 17:32:50 c7eee74e [app] [I] Current user: admin (administrator)
2017-10-23 17:32:50 c7eee74e [app] [I] Failed to save:
2017-10-23 17:32:50 c7eee74e [app] [I]   Rendered taxonomies/_loc_org_tabs.html.erb (0.1ms)
2017-10-23 17:32:50 c7eee74e [app] [I]   Rendered auth_source_ldaps/_form.html.erb (13.8ms)
2017-10-23 17:32:50 c7eee74e [app] [I]   Rendered auth_source_ldaps/edit.html.erb (14.3ms)
2017-10-23 17:32:50 c7eee74e [app] [I] Completed 200 OK in 27ms (Views: 14.8ms | ActiveRecord: 3.6ms)
2017-10-23 17:32:51 cdd5557a [app] [I] Started GET "/notification_recipients" for 172.16.28.83 at 2017-10-23 17:32:51 +0300
2017-10-23 17:32:51 cdd5557a [app] [I] Processing by NotificationRecipientsController#index as JSON
2017-10-23 17:32:51 cdd5557a [app] [I] Current user: admin (administrator)
2017-10-23 17:32:51 cdd5557a [app] [I] Completed 200 OK in 4ms (Views: 0.2ms | ActiveRecord: 0.8ms)
2017-10-23 17:32:54 68919a36 [app] [I] Started PATCH "/auth_source_ldaps/3-example1" for 172.16.28.83 at 2017-10-23 17:32:54 +0300
2017-10-23 17:32:54 68919a36 [app] [I] Processing by AuthSourceLdapsController#update as */*
2017-10-23 17:32:54 68919a36 [app] [I]   Parameters: {"utf8"=>"✓", "authenticity_token"=>"pJwt/8FZnAT70vYI+EyK2As8a5oM4pFSQmIOOIXPWP7a8jCVlyA89OfQC4Y3aeQjQXMxiVmyktpxe8KlEDlyMA==", "auth_source_ldap"=>{"name"=>"example1", "host"=>"example.ru", "tls"=>"0", "port"=>"389", "server_type"=>"active_directory", "account"=>"ad_auth", "account_password"=>"[FILTERED]", "base_dn"=>"DC=example,DC=ru", "groups_base"=>"OU=Security Groups,DC=example,DC=ru", "use_netgroups"=>"0", "ldap_filter"=>"memberOf=CN=puppet,OU=Security Groups,DC=example,DC=ru", "onthefly_register"=>"0", "usergroup_sync"=>"1", "attr_login"=>"userPrincipalName", "attr_firstname"=>"givenName", "attr_lastname"=>"sn", "attr_mail"=>"mail", "attr_photo"=>""}, "_ie_support"=>"", "id"=>"3-example1"}
2017-10-23 17:32:54 68919a36 [app] [I] Current user: admin (administrator)
2017-10-23 17:32:54 68919a36 [app] [I] Failed to save:
2017-10-23 17:32:54 68919a36 [app] [I]   Rendered taxonomies/_loc_org_tabs.html.erb (0.1ms)
2017-10-23 17:32:54 68919a36 [app] [I]   Rendered auth_source_ldaps/_form.html.erb (16.3ms)
2017-10-23 17:32:54 68919a36 [app] [I]   Rendered auth_source_ldaps/edit.html.erb (16.8ms)
2017-10-23 17:32:54 68919a36 [app] [I] Completed 200 OK in 33ms (Views: 17.4ms | ActiveRecord: 4.3ms)

Any news about fixing of this issue? After upgrading to RC2 the problem is still exist

Marek Hulán wrote:

Is this active directory? If that's the case, it's most likely cause by #21175 which should have been cherry-picked but most likely was not as I noted at https://github.com/theforeman/foreman/pull/4885#issuecomment-340074271. Daniel, I'm setting the release here to 1.16 which should hopefully help to get this in.

Al, thanks a lot for testing RC. It would be great ff you could also try to apply the patch from #21175 manually to confirm it fixes the issue.

Yes, you are right, it's AD. I applied this patch and it solved this issue. Thank you, Marek!

Thanks for confirmation! Keeping this open as a 1.16.0 blocker.

This was cherry-picked to 1.16.0 (RC3) as https://github.com/theforeman/foreman/commit/e1f6d739573b49dfa641fd5c2cc1af173340403e, closing