Artist 11 Notes hanging in MIDI Editor / Step

I have Cubase Artist 11, and have a problem when using the MIDI editor. Playing notes in via step for an external synth either have notes not playing or hanging and requiring a reset. This only happens with my external synths and doesn’t appear to happen at all with any soft synths. It only happens in when entering things in via step sequence in the MIDI editor. Playing in live it doesn’t do it. No double notes appear to be entered. Only one MIDI driver is in play. I’ve tried 2 seperate keyboards to enter in editor (an AKAI MPK Mini mk2 and an EMU X-Board 49). It’s only started happening since a fresh install of Windows 10 and the newest version of Artist 11. It’s driving me insane!