I’ve encountered this on occasion, but it seems to be happening too much on my current project…
Undo is not working on note input. It works on everything else besides note input. For instance, I just wrongly inputted a rhythm, hit undo, and it did nothing, but DID apply the undo to text I added before inputting the notes.
In case my recent experience may apply: A few times I have seen Dorico 4 hang for more than a second, with no visual indication, and then I get a very brief “wait” cursor and it catches up. I have learned to wait a moment when I don’t get the expected response to a simple command, instead of trying again or trying something else immediately (which then goes into the queue of actions and things get confusing quickly).
I should restart too. Dorico has crashed enough times (harmless in itself) that I probably have memory remnants from abandoned instances of the VST Audio Engine.
And yesterday I had a Dorico project, which - when I pressed cmd-S (for Save) - did actually save, but at the same time Selected All, (=each time I pressed cmd-S, everything turned orange).
I then closed the project, when reopened the problem was gone.