Queue "drops" calls

Hi,
I have a problem with my new queue dropping all but the first call.

So the scenario is:

Calls get onto the queue as expected.

All agents are ringing. Nobody is on the phone

2 or more calls are sitting in the queue and they can remain there indefinitely (or when the max wait time is reached - they are then correctly handled)

However if one of the agents answers a call then all the other calls on the queue are dropped.... in my case they are dialing 2083 on an outgoing trunk. WEIRD

Only the one (first) call is handled correctly.

Nothing changes if I use different agents (SYSLINK SPA941, Netcomm V85, Idefisk soft client).

I have also configured another queue from scatch and the same behaviour is repeatable.

What do I do?
Is there a bug?
Do I need to set some divert on the agents?

Don't know where to go.