Hello, I agree with Max Jansson, it would be "re-roll all dice that have not yet been assigned to a space(no exceptions)".
I have a question about return units from scanners in this ship(Athena Mk. II), in the rule book area for all ships you can read "Units returned from the infirmary or scanners...", so I was assuming that it would be possible in all ships to return units from scanners, but in this ship it's not possible or I'm missing some thing.
Units are returned from the scanners after they have filled all the slots and revealed a new threat. Some effects may return them before this happens.