"Samsung keyboard keeps stopping" error message. After reboot no keyboard is accessible and I cannot unlock the device
Enable Emergency Mode. This shuts down to only essential services. 

This reverts the device to the default Samsung keyboard and will allow you to enter the password. 

You can then disabled Emergency Mode go into the settings and re-enabled Swype.

Source:

https://androidforums.com/threads/samsung-keyboard-keeps-stopping-locked-out-of-phone.1166997/#post-7579781