I’m finding that undo is not working consistently in Dorico if it’s been running for a while, and I see similar comments in the Nuendo forum.
Some things can not be undone in Dorico, such as pasting lyrics. Is this the problem you’ve had? Otherwise, I don’t think I’ve seen anything like that. Can you be more specific ? We Dorico users are not all using Nuendo, obviously (nor do we read the Nuendo forum).
Nuendo and Dorico have very little in common, beyond the fact that they use the same audio engine (though they use it in very different ways) so it’s vanishingly unlikely that there would be anything more than coincidence at play if you are having problems with undo in both applications.
Can you be more specific about how and when Dorico fails to undo?