I had the same problem, this fixed it:
1 Shut down your Mac.
2 On your built-in keyboard, press and hold all of the following keys. Your Mac might turn on.
• Control on the left side of your keyboard
• Option (Alt) on the left side of your keyboard
• Shift on the right side of your keyboard
3 Keep holding all three keys for 7 seconds, then press and hold the power button as well. If your Mac is on, it will turn off as you hold the keys.
4 Keep holding all four keys for another 7 seconds, then release them.
5 Wait a few seconds, then press the power button to turn on your Mac.
kpaj
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