Cubase pro 10 constantly crashes when using external instrument


I have Cubase Pro 10. And I recently bought a JP 8000 synth.

I have created an external instrument from 2 mono inputs (from the Audio interface I have where the JP is plugged into).

It worked yesterday. I could play the piano roll and hear the JP8000. And I could play the JP8000 and see input coming in (record midi notes) etc.

But now it constantly crashes whenever the instrument track with the external instrument is used. For example if I click in the piano roll from that instrument track.

I have zero idea what to do… Does anyone have an idea?