You assume it's just a software glitch - obviously some weird reflections or something confused the range finder, and the vacuum's mapping algorithm interpreted the data as a whole second room or hallway.
Sometimes the map shows that the vacuum has actually entered the non-existent space and is cleaning there, but obviously that's just the position tracking also screwing up, so it thinks it's somewhere far away and just maps it to the closest place it thinks exists.
The map keeps growing, though, and the vacuum's taking longer and longer to clean the whole house.
Eventually it's frustrating enough that you start setting aside time to watch it do the cleaning, so you can figure out what surface is confusing it and fix the problem.
Somehow the problem never happens when you're watching.
The vacuum seems more beaten up than you remember - scratches and small dents, nothing to stop it from working, but you're not sure where they came from.
Once, you look while it's cleaning and can't find it anywhere. The mobile app says it's cleaning the living room, but it's obviously not there. The app is often wrong, though, and when you hear it trundling around the dining room, which you just checked, you guess you must have just... missed it somehow?
When you empty its bin, there's strange, golden dust in it that you've never seen before.
You install a few cameras. Every time the vacuum malfunctions, it's always when it's behind something or in a dead zone between cameras. Even when you move the cameras. It's a different place every time.
Did you spill ketchup somewhere? There are desiccated flecks of brown and red in the vacuum bin.
You get a Bluetooth tracker - it's supposed to help you find your keys or your wallet if you misplace them - and you glue it to the vacuum.
That night, the vacuum has a new scrape on it, like it ran into something, and the tracker has been knocked off. You can't find it; the tracker app just says it's "out of range or turned off".
You look at your robotic vacuum. It's got more scratches and scrapes even than you remember from a few days ago. You check your camera footage and yeah, it's definitely gotten more beaten up. No footage of it running into anything, though.
One of the dents almost looks like a... bite mark? You must be imagining that.
You sit and think for a long time. You know it's just a machine; you know humans tend to anthropomorphize anything that moves (all the more so because of the googly eyes you attached when you got it), and you don't want to fall into that superstitious fallacy.
You look at the dents and cuts on its frame.
You sigh, turn off the cameras, and duct-tape a kitchen knife to the robot.
"Just don't scratch up the sofa." you mutter, feeling silly, and press the "clean now" button.
The startup beep is the same noise as always, and you tell yourself there's no way it could possibly sound 'excited'.
