An endpoint can register without being eligible
Queue membership, pause state, penalty, device state and active-call policy contribute to agent selection. A registered phone is merely reachable for registration purposes; it is not proof that the queue will select it for the next caller.
Start with one queue, one waiting caller and one expected agent. Record the exact time and the member identity. A display name is less useful than the configured interface when two devices belong to the same person.
Inspect the running queue
Use queue show in the Asterisk CLI to inspect current members and callers. Compare the runtime state with the intended configuration. Check the installed help before using membership-changing commands; adding or removing agents changes live call handling.
In FreePBX, use supported GUI or documented dynamic-agent controls. Directly editing generated queues configuration can be overwritten and leave the administrator comparing two different sources of truth.
Reproduce the eligibility boundary
Test the same member idle, busy, paused and logged out. Observe when the caller overflows and whether the timer applies to each attempt or the overall wait. With penalties, do not assume an available low-penalty member will be bypassed simply because that person did not answer.
If the queue selects the interface but the phone never rings, move to endpoint and SIP diagnosis. If it never selects the interface, inspect queue state first.
Preserve operational evidence
Collect the queue state, relevant queue log events and call identifiers for one reproduction. Keep caller information private. Update agent procedures when the cause is stale login or pause state instead of compensating with increasingly complex ringing rules.
Sources & applicability
Primary references for the technical details above. Operational examples and planning checklists are VoIP.info editorial guidance.
Examples require adaptation to your topology. No live PBX or hardware testing is claimed.