"Wrong Pattern" After Flashing Image
Note that @dan-brown seems to be right about the root cause of the issue - it looks like a corrupt install after flashing a new TWRP.

However there is a non-destructive fix, as documented here.


Boot into recovery 
Navigate to /data/system
Delete the following files:


password.key
pattern.key
locksettings.db
locksettings.db-shm
locksettings.db-wal 

Reboot