Nasty bug: I lose undo, cannot do anything to tracks recorded after bug hits. CRISIS!

I’m on 9.5, and I am struggling with the following bug, which, in fact, I also encountered a couple of times with Cubase 9, but occurs more frequently now:

After a while, I lose undo. I cannot undo, cannot use history and go back, and cannot do anything to tracks recorded after the bug hits. Not highlight, not delete, nothing.

This is a complete showstopper!

It goes away if I restart Cubase. The problem is on new projects and old projects alike.

Has anyone encountered this?

I don’t want to “nuke” the system, and go through all the migraine-inducing troubleshooting stuff (uninstalling plugins, rolling back Windows versions etc.)

Is there anything quick I can do?

My system:

Windows 10 home (latest update, no change after update to creator’s)
Intel i7 920
16 gb ram
Steinberg UR 28M sound card
Plugs include
EastWest composer cloud
Addictive drums and keys

Oh, and I just tried loading without my preferences (“safe mode”), and now the bug hits right away. I have Cubase without undo. 100% useless… Help!

I can see the history, but not roll anything back. Plus all the events created cannot be highlighted or edited.