asterisk users - Jan 2019 - Out of queue - no pickup after 0ms

Hello,

I have an external agent which register dynamically in a queue and I 
setup his PJSIP account on a identity of a local phone which is 
configured to redirect all calls to the agent. Agent can have only on 
call at a time.

When agent takes a call he is paused from the queue to avoid further 
dial from the queue has his state is always "Not in Use". What happend
is that after having taking a call, the agent is unpaused and should get 
next call in the queue. But what I see is

app_queue.c: Called PJSIP/exten115
app_queue.c: -- PJSIP/exten115-00000620 connected line has changed. 
Saving it until answer for PJSIP/TOOTAiAudio-00000612
app_queue.c: -- Nobody picked up in 0 ms
  [many times]

What does this mean ? TOOTAiAudio-00000612 being the caller channel in 
the queue, the callee channel increase on each try. The callee is well 
known to be idle.

app_queue.c: Called PJSIP/exten115
app_queue.c: -- PJSIP/exten115-00000621 connected line has changed. 
Saving it until answer for PJSIP/TOOTAiAudio-00000612
app_queue.c: -- Nobody picked up in 0 ms
app_queue.c: Called PJSIP/exten115
app_queue.c: -- PJSIP/exten115-00000622 connected line has changed. 
Saving it until answer for PJSIP/TOOTAiAudio-00000612
app_queue.c: -- Nobody picked up in 0 ms
app_queue.c: Called PJSIP/exten115
app_queue.c: -- PJSIP/exten115-00000623 connected line has changed. 
Saving it until answer for PJSIP/TOOTAiAudio-00000612
app_queue.c: -- Nobody picked up in 0 ms

delay between tries being around 5 seconds.

Other question, is it possible to tell to a queue that a member is in use ?

Asterisk version is 16.1.1

Thanks for any hint

-- 
Daniel