it seems like the Roombas have a habit of just... leaving. Not super common but my first try it happened immediately and I was so confused, and on my second try I've seen it happen a couple times, though I have more Roombas here luckily.
edit: on my current save the new roomba upgrade is lvl 10, and I got a screenshot and counted 11, so it seems fine, but I def lost it on 1st save