I ran into an issue where I was moving my Queen with multiple hires available due to changes mid-travel.
The Queen is set to arrive during the night, so I wanted to queue up the correct hires and was able to hire two in the future but it won't show me any more. In fact, if I use one of them on a promotion I am only able to hire a single specialist before it stops showing me any as being available. (I can hire two, then promote however.)
This seems like a bug because these are 'banked' hires I already have in the present, so I should be able to see what they are after my queued hire is available.