The ticket I just reserved my seats on is actually Q, which is mega low internet offer.
Elite helpdesk told me that Cityhopper would not be a problem on reserved seats for elite members but only intra european from AMS.
They told me you can only get a seat confirmed on intra european at the check in, so first come first served.
I missed my connection last week in AMS and got a seat allocated for the next flight some 20m hours later.
Again it is mis-information and the left hand does not know what the right hand is doing.
Try the UK sales office number and see what they can do as they are usually pretty helpful