A few of things here:
1) When setting up a session, the driver names in the map view do not coincide with the actual names of the drivers assigned to the consists.
Harry and Geoff are assigned here to unassigned consists.
Kenny, Sean and Sean are assigned in the map view to consists actually "owned" by Basti, Lukas and Bob.
View attachment 1972
View attachment 1973
2) When assigning drivers to consists, the placed consists do not always appear in the available consist list.
Have also seen this happening in build 105100 you set up drivers in session then they change in driver to someone else
Didn't worry about it as I only found it just before current build released