I just spent the last few hours sorting out my mac. I accepted the latest os upgrade for my 2013 MacBook Pro 13 inch.
Then promptly lost use of my external USB keyboard.
The only way I can now use it is via my thunderbolt dock. Ie plug keyboard into the dock, and dock my MBP.
this was th solution after searching the web.
It seems to be something to do with the switch over to USB c , and a bug.
So just a heads up