Sometimes it is experiencing a playback frozen: the sound is played back as normal but the interface get stuck. And it can not be stopped either by cllick the transport tool bar or the external midi controller.
Could you try in Cubase Safe Start Mode?
I haven’t hear about this issue so far, so it doesn’t look like a global issue.
I have had the exact same problem since Cubase 9 (not totally sure, but I think its was 9). Havent been able to find out why it happens. Every now and then, Cubase freezes but playback continues. The video keeps running, Cubase keeps playing, but there is no way to unfreeze it, meaning I have to Force Quit every time it happens.
I’ve tried to test this on Cubase 10, but unfortunately it kept doing weird things with respect to the GUI colors, so I am back to 9.5. Will test it someday when I have the time.