I suggest all who are going to flash beta from stable to change their lock screen password (patterns and passwords) to pin (numerical value) in beta rom. So when u r switching to stable rom then u will be asked with to enter your pin at that time u can enter that pin which u have set in beta rom. So u will not face that 'confirm your password' issue in poco f1. I have switched to 10.3.4. stable from beta 9.6.13.