If I press ‘esc’ in (mine) demo board I enter a mode where I can’t place any stones. Seems like a bug.
Serves you right, escaper.
It deselects the tool you’re using and jumps back to the original empty board state. If you click on a tool, you can place stones again. Not sure how useful it is to deselect (as opposed to just changing) a tool, but ‘back to the beginning’ seems warranted.