I would imagine what happened was the metal piece attached to the rubber part that gets pushed onto the sensor got too much glue. (not sure how else they would get those metal pieces to stay on the end of that rubber, considering glue was present). Either that, or there was an accident at the Digimon factory.
But yes, I prefer to take care of 1 at a time. I tried raising 2 at a time, in the group hatching I hosted at the beginning of the month. But that had a share of problems between both of them requiring different care, and the rate these things poop at is so high, 4 piles of it gets piled up quicker when you have 2 going on the same device. Being that I am older, I prefer things more simple, and trying to care for 2 on the same device (even with multiple devices at times) becomes confusing and harder to keep up with.