Suddenly, undo and history no longer work!

Have just started a new project from scratch, using Play from EastWest and a few Cubase plugs.

While editing the drum track (first double-click, and then undock the drum editor, I discovered that undo no longer works. I see the events in History, but can’t go back.

This is potentially catastrophic if it happens on a real project, not just something I spent an hour creating just to play around with Cubase 9.

Can’t reproduce it as such, but the history remains frozen in this project.

Using Cubase 9.0.0 build 92

Update: I can undo again when I open the project. This bug will still be extremely annoying if I have to close and open huge projects often.