Same problem here trying to run a Quantum Sequencer when Cubase is stopped. Are you using MIDI DIN or USB ? The Synths I have running USB MIDI seem fine except for a short freak out when you stop or start, otherwise they get the clock when stopped. Only anything on a DIN connection won’t. I’m running USB to a Komplete Kontrol S88 then out the MIDI port to the Quantum. I suppose it could be the S88 stopping it after the stop command …