Twice in the past three days, my 2013 27" iMac started typing all keys as if the option modifier was being held down. I don’t think it’s a bad keyboard, because I unplugged mine and connected a Bluetooth keyboard, and the problem was still there.
I first noticed it when I tried to Cmd-Tab to switch apps and nothing happened. I have to restart to get back to normal. I reset the PRAM after the first incident, but 2-3 days later it happened again.
I’m suspicious of the Karibiner Elements app, since it’s the only thing I know of that’s taking liberties with the keyboard. But I’d been using it for 2-3 weeks before this happened, and the only thing I’ve done with it is set up the caps lock as the Shift-Ctrl-Opt-Cmd hyper key.
Other items in the mix: Keyboard Maestro, Stream Deck, and Text Expander (but its expansion was disabled when this happened)
Any ideas? This is a little frightening.