Command+{key} shortcuts are intermittently repeating, and keyboard is lagging intermittently too (although they don't repeat keys)

xThomas wrote:

I am using a Magic Keyboard.

Could it be something wrong with my command key? it could sorta explain the repeating keys, maybe if the CMD key got stuck for a second when I press it sometimes.

I should be able to test that with the right-side CMD key, just haven't bothered to yet.

That wouldn't explain the lag though, which I see as possibly a separate issue.

Report back your findings

—"I should be able to test that with the right-side CMD key, just haven't bothered to yet."

To trouble shoot further you can:

—Test issue in another user (or guest user) account Change Users & Groups settings on Mac - Apple Support

This will tell you if it a universal issue or isolated to your user/admin account. 

—A SafeBoot How to use safe mode on your Mac - Apple Support will sort many anomalies

This test will tell you if third party interference; most* extensions etc are not loaded in safe boot mode.

ref: How to clean the keyboard of your MacBook or MacBook Pro