I am very sorry to hear about your Scooter. It is always very hard to loose our dear pets, but when it happens unexpectedly it is terrible.

At my shelter we had one or two very young kittens who suddenly died, but they were not very strong and fighting to survive so it is different.
But three days ago an adult cat among the permanent residents (he was not social with humans so he could not be adopted) suddenly died. He was 4-years old. We found him half-way out of the litter box. One hour before he was perfectly OK...an autopsy has been made and we wait for the results. We were all shocked.

And some years ago a friend of mine suddenly lost her 8-year old cat (also apparently perfectly healthy). He was sleeping on an armchair an never woke up.

These things also happen to humans, even young. For the kitty who died three days ago, I prefer to think that he had a pretty good life and that he could have died in much worse conditions (disease, ...). I am sure your Scooter had a happy life too and he would not want you to be too sad