Bad days happen, offensively and defensively. It doesn't matter who you are.
I am in no way comparing them, but Brooks Robinson made 3 errors in a game at least a couple of times. There was one game when he made 3 in one inning. As I said, those games happen.
Devers has been trending upward defensively from what I've seen. He is far from a finished product. I doubt he will ever be in the conversation for a gold glove, but he is getting better.