In RPG Maker you can set moving routes for NPCs. The engine waits until the NPCs reaches his destination, no matter what. If a moving route is blocked by anything (e.g. the player) the game freezes. That's a stupid quirk of RPG Maker, because it quickly introduces game-breaking bugs, if you are not carefully.
In this case, the maid boss wanted to move downwards and was blocked by the player. I have now activated a routine that ensures the game continues even if a movement route is blocked. So the bug will be gone with the next upload