Maestro should not be asking POP/DN serial number especially when you are migrating to the same maestro instance.
Can you share the techdump to get more details on it.
POP node coming online but other node not coming online is probably a recipe where controller is not able to route packets to the prefix address which gets assigned to CN and DN.
We need to add static route for prefix address in controller to POP address or enable auto manage route feature which will take care of adding and managing these routes.