Mirko from QM support helped clear this up for me. Here is an explanation in case anyone else has the same question:
the problem here is that the report period should contain the agent's log in
event. Otherwise QueueMetrics can't know which agent has handled the call.
I mean, when an agent (say agent/101) logs in the queue, he tells QueueMetrics
which extension he will use (say SIP/200). So QueueMetrics will write on
queue_log a custom line "HOTDESK" which tells: "for this session SIP/200 is
used by Agent/101").
If you run a report which doesn't contain the HOTDESK report QueueMetrics won't
know that SIP/200 was used by Agent/101.. what will happen is that if you
filter by agent/101 you won't see any call because, yes there calls handled by
the phone SIP/200, but QM doesn't know that SIP/200 is Agent/101
Mirko