My Brew Monk switches off while I'm brewing.

This is the boil-dry protection that automatically switches off the heating element, because the bottom has become too hot. The Brew Monk needs to cool down first, before this message is reset. One potential cause is that the grain is crushed too fine, causing particles to burn on the bottom, resulting in generating too much heat. Another possible cause could be that the bottom is dry when pumping the wort. This can be remedied by slightly closing the tap of the circulation pipe, so that a slower circulation speed is maintained.