I had a key command issue with “bounce selection” as the system was unresponsive. That’s until I figured out that the onscreen keyboard in Nuendo / Cubase filters certain keys (including all F keys like F1, F2 aso). The onscreen keyboard wasn’t event visible or “onscreen” or activated by me, yet it didn’t let the commands through. I had to activate the onscreen keyboard, then deactivate it using Alt-K. Only then was the issue resolved.
I wish there was a Nuendo / Cubase setting in the preference to just deactivate the onscreen keyboard globally. I will never use it in the studio, so all it does is get in the way of my work flow.