I'm trying to nail down a problem I'm having with my Mac: when I depress the CMD key, the 2, 3 and 4 keys on the top row of the keyboard are unresponsive; on the number pad, CMD+1-4 are unresponsive.

I find it's also occurring on my MacBook Pro, although it's only CMD+3 and CMD+4 which are affected.

I've discovered this in trying to make use of menu items in Mail, Safari, Finder and Ulysses which are supposed to be activated by these shortcuts the menu items work find using the mouse, it's just the keyboard shortcuts that appear to be broken.

It's definitely a software issue. It seems to occur only on my account. I've tried cleaning, safe-booting, removing plist files, changing keyboards, changing USB inputs everything I can think of and find on the internet, but nothing has resolved it. Perhaps I've installed and possibly long-deleted something, or changed a setting and forgotten, but it's really got me stumped and I'd like to sort it out.

Does anybody have any ideas how I might fix this?

Many thanks.