How to recover from a brown out on STM32L0
The micro core will work at 1.65 but the peripherals will not all work below 1.8V. With 1.8V supply there is no headroom between when the BOR trips and where the micro misbehaves. Setting the supply to 2.5V and the BOR to 2.2V gives some time to react before the supply reaches 1.8V and will have better noise immunity. 1.8V regulators have a tolerance. some will give slightly less than 1.8V and so some boards will misbehave if you build enough. Choose a regulator from 24V with a defined enable voltage and set the regulator to switch off at a much higher Voltage using a potential divider on the enable input. The supply will only be there when it is stable.