Just Post

I don't claim to understand the mapping program of any of these robots.

However, for mine, my interpretation is that the map shows what it sees (or thinks it sees) rather than necessarily where it's been. If where it is isn't where it thinks it is and it sees an empty space ahead, it will think it saw a room where there was none.

I couldn't say if that's what's happening here, but it is what has happened to me.