As far as I have seen in this forum in the past, you can't apply for passport before your status becomes complete. But who knows
For passport application having the citizenship certificate matters more, meaning a person having a citizenship certificate is formally "done" with the citizenship processing.
At this point the ECAS not reflecting the correct citizenship application status is due to the fact that the officer handling the last stages of the citizenship application processing has not completed their standard operating procedure of ticking/clicking somewhere in the ECAS system to "complete" the process in the system but have already released the official document.
Anyway in the current situation with normal passport applications being accepted only through mail and the slow processing rate, by the time the passport application reaches the "print/issue" stage, the ECAS status would get updated. In an emergency/urgent scenario the ecas status really doesn't matter and the passport is being given based on the criticality of the candidate's situation.