I have a queue, that has virtual agents (FMFM to off PBX numbers, landline, IP, cellphone), and it works just fine. When I turn call confirm (press 1 to accept), sporadically, it will not connect the caller and the agent. Users are reporting they hit 1 and it fails to answer/connect. I turn it back off and it is fine again. There is two-way audio, what else could it be. We need call confirm turned on to avoid going to users personal voicemail boxes.
Do you have logs of a call example? First guess would be that by the time the user pressed 1 the caller had hung up or the ring timer had been reached.
Try increasing the Agent Timeout value on the Queues > Timing and Agent Options tab > Agent Timeout. Give the home agents a little longer for the call to process through to the agent and be picked up. This will probably solve your issue.