I doubt midi controller and midi keyboard are different things for Cubase.
Bluetooth - what an unusual decision. People are fighting to get as less latency as possible with their MIDI instruments and buying audio interfaces with MIDI ports, but others are using Bluetooth. Interesting. There’s no borders to markings’ bullshіt to make people buy their products 
O.k. now seriously. I don’t think it’s Cubase problem. I have some keyboards and controllers or keyboards and controllers combined but Cubase are opening projects fine. Maybe it is waiting while Bluetooth connection initializes or receiver makes it to wait. Ask some acquiescent to borrow you a generic wired MIDI and try connecting it.