I've recently run into the same issue. Computer screen locks while connected to external screen, using BT keyboard and mouse. I enabled Touch ID, but with the external screen connected, I can't access the button for the scan, so I'm prompted for the password input. After entering the password, the field becomes grey, and the system locks up. Have to hard reboot after that. I'm wondering if it's due to the Touch ID trying to activate, but not being able to.
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