ACD - Second Agent won't ring

[John]

Hello,

I have the following setup for a customer:

Auto Attendant with a DID assigned to it and dtmf options configured. The caller hears the welcome message and presses the key to connect to the department he wishes to. The Auto Attendant redirects the incoming calls to 3 agent groups depending on what key the caller pressed. Each agent group has 2 agents, all of them logged in and available. The "Number of agents added per stage:" is set to 2 (basically we want the agent groups to act as hunt groups but with music on hold and messages for the callers in queue).

2 of the 3 agents groups work as they should. If both agents are available, their phones will ring simultaneously. In the third agent group however all calls are always sent to one agent only. The second agent's phone never rings. For some reason the pbx consider the extension as unavailable. From the logfile:

[7] 20150414152709: Call 17178: [ACD 9101] Next stage in 9101 has 1 agents available, 483 selected

The other agent (484) though is available (I also made sure that dnd is disabled both in the pbx and in the phone).

• Both users use Yealink T20P phones with the same firmware - 9.73.0.40.
  
• Even if I register more user agents for the second user, his extension won't ring.
  
• If I set another extension as the second agent and call through the Auto Attendant, both agents will ring.
  
• If I assing a DID directly to the agent group and call it, both agents will ring (agent 484 too).
  
• If I set "Allow multiple ACD calls on agent - even if busy:" to yes both agents will ring.
  

So, what are the possible reasons that make the PBX (v 5.2.5) to inccorrectly consider this specific extension as unavailable?

Regards,

John