3. Age

David Raya is currently 28 and turns 29 this coming September. While this is not particularly old for a goalkeeper, it also isn't young.
As has been shown in the past, some keepers have gotten worse with age whereas others have improved. Unfortunately, with his mistakes, Raya is already showing glimpses of a weaker ability between the sticks.
Due to his age, he certainly won't be Arsenal's number one choice for years to come and there is potential that he could be replaced by a younger and better prospect in the future.