Since upgrading to kubuntu 21.04 every now and again the keyboard stops working for _all_ konsole windows running at that moment.  

New windows work fine, new tabs in the same window do not work. New tabs subsequently detached don't work either.

The keyboard still works (I'm typing this) for other programs and new konsole windows.

No keyboard activity goes to the shell and it seems no keyboard activity goes to the menus either (but the shell keeps running and the screen updates just fine). I tried changing the key bindings in a keyboard-dead konsole - makes no difference (everything you can do with a mouse works, middle button paste works).

I've tried to associate this with something I've done but I see no pattern except perhaps (long shot) adjusting the panel in some way or changing the appearance settings but it's hard to tell.