I found a bug with station managers. I have a problem whereby I cannot assign a manager to 3 of my stations. All the others I have done successfully so I understand the mechanic. It manifests when a station requests a manager and has none assigned, but you get a message saying "This person cannot be employed at......".
After many hours of rebuilding stations, trying to reassign other crew etc. I found the problem was the manager never got off the ship from which they were assigned. Therefore a manager for my station could be on a scout ship the other side of the galaxy, the station wouldn't operate and nor could I assigned another manager. The station would also show no manager as being assigned.
The manager on the ship did not show in the ship roster either, it was only by physically boarding the ship myself I noticed.
The only fix I could find for this was to leave the ship and destroy it, killing the manager. I could then assign a new one successfully.
This is still an issue though, as I have two stations to which a manager is assigned but not present (and not showing on crew list for station), but I have no clue on which of my ships they might be hiding

I'd really like this addressed in an upcoming patch, as I see from the forums I'm not the only one to experience the issue.
Hope this helps.