Why are our 6.4.1 universal forwarders unable to connect to a new 6.4.1 deployment server on Windows?

Hello, I have a new deployment server (also acting as search head) installed on Windows Server 2012 R2 with version 6.4.1. I have multiple Universal Forwarders installed on misc Windows OS (2008 R2, 2012, 2012 R2) with version 6.4.1 Deployment Server is enabled (confirmed with Splunk CLI), has a local serverclass.conf, a deployed app (TA_Windows), all looks fine from Splunk Web. All UF are enabled as deployment client : deploymentclient.conf [target-broker:deploymentServer] targetUri = :8089 Required firewall ports are opened, and I confirm server is listening on tcp/8089. However, none of the clients are able to handshake with the server (even those on same subnet than server). Enabling DEBUG log, I see the following on client side : 06-04-2016 07:37:01.962 +0000 DEBUG DC:PhonehomeThread - PhonehomeThread::main top-of-loop, DC state=Initial 06-04-2016 07:37:01.962 +0000 DEBUG DC:PhonehomeThread - Attempting handshake 06-04-2016 07:37:01.962 +0000 DEBUG DC:DeploymentClient - Sending message to tenantService/handshake 06-04-2016 07:37:01.962 +0000 INFO DC:DeploymentClient - channel=tenantService/handshake Will retry sending handshake message to DS; err=not_connected 06-04-2016 07:37:01.962 +0000 DEBUG DC:PhonehomeThread - Handshake not yet finished; will retry every 12.0sec 06-04-2016 07:37:01.962 +0000 DEBUG DC:PhonehomeThread - Phonehome thread will wait for 12.0sec (1) On server, nothing very useful... 06-04-2016 07:22:53.222 +0000 DEBUG ClientSessionsManager - After running metrics, |_newClients|=0 |_existingClients|=0 06-04-2016 07:23:24.223 +0000 DEBUG ClientSessionsManager - Before running metrics, |_newClients|=0 |_existingClients|=0 06-04-2016 07:23:24.223 +0000 DEBUG ClientSessionsManager - After running metrics, |_newClients|=0 |_existingClients|=0 06-04-2016 07:23:55.222 +0000 DEBUG ClientSessionsManager - Before running metrics, |_newClients|=0 |_existingClients|=0 Any idea? This is a brand new install. I already did a similar setup in the past and it works without problem. Servers are new, this is the latest Splunk version, but I cannot see any other difference. Thanks.