left cmd + z not working

I can't undo with shortcut combo 'cmd + z' in all apps. I think it might have started after update to Mojave, but I'm not sure.

Here are some deets:

- The z key and the left cmd key work by themselves--I can type a 'z' and I can use command key with other combos like c, v, n, etc.

- The right cmd + z works.

- The undo command from app menu works in all apps.

- When I pull up the Show Keyboard Viewer, I can see the each key light up when pressed separately. If I press left command first the 'z' won't light up, and if I press the 'z' it will light up but when I press left cmd the 'z' will become unlit and left cmd with light up. Works normally with right cmd + z.

- Problem still occurs in Safe Mode, and in Guest user account.

- I have been having problems once in a while where the 'z' key is not responding, but will work after I press it once or twice.

Things I have tried:

- Showing keyboard and emoji viewer in menu bar (Not sure how that was supposed to help but read it in post.)

- Restored defaults in keyboard shortcuts, and made sure it was not being used for any other function like voice over.

- Reset PRAM.

Any ideas. This is driving me bananas as of course I have to undo a lot.

Thanks!