When a placeholder connector is created, an import is done to import the container object into FIM such that it can subsequently provision objects back out to the placeholder connector.
When doing an Identity Broker migration between environments by way of config migration, there was a bug where FIM would report that - when trying to run the import to get the container object; there was in fact no objects to import.
Did a bit of digging, ended up changing the Container Name in the placeholder connector in IDB to something different, saving connector, and then changing it back - and then running the import into FIM. Upon doing this, the container successfully imported.
It seems like it stores something in the database as an entity for the container (logically) and when you migrate, this does not get copied across (logically). However a rename triggers this entity to be created and thus picked up by FIM when the import is run.
Customer support service by UserEcho