Hi,
this can be caused by misconfiguration of the device, eg call forward, remote device, shared line or something like that.
In other cases we have seen this at smaller locations with less bandwidth or codec missmatch configured.
You can also try reassigning the phone to the jtapi user. Sometimes this helps, too.
When the agent does not receive the call, only signaling in Finesse via CTI, it means the call cannot be delivered to the agent for some reason.
Hope it helps, please let me know your findings.
Dennis