Announcement: Upgrade to macOS Mojave
Next time you turn on your mac, go to About This Mac > System Report... > USB
And see if there's anything weird.
Also check System Settings > Keyboard > Input Sources
Also check the other tabs for anything unusual.
If you don't find anything consider running https://EtreCheck.com
It's free and doesn't ask permission/install anything. It will run a system report looking for anything unusual.
If you copy/paste the results here we can check for problems. Nothing personal is shared.
I think someone from these forums wrote the program.
Restart the computer holding down the command - option/alt - P - R keys before the gray screen appears. Continue to hold until you hear the startup chime for the second time. You may need to do this 2-3 times.
Try a SMC reset. The article covers when this is required, but doing this will not affect anything.
Question: Bug within Mac OS Sierra?