Are you calling the workflow using an asynchronous <call> activity and using a <sync> activity to wait on it? For how long is your <sync> activity waiting? Beware that a workflow task will only stay on the workflow inbox while that <sync> activity is not done. So, if you don't have a <sync> activity or if the timeout on the <sync> activity is too short, the task will not appear on the workflow inbox or appear only momentarily.
The idea is that the BPL can put a timeout as an SLA on that task. If no one finish that task until that timeout expires, you will receive whatever (incomplete) response is there and, maybe, escalate to other roles, send alerts, etc.