Dog Peeing and Pooping Inside at Night?

I just got a new dog he is a toy Poodle. He is 3 years old and I have had him for about 4 weeks now. He hadn't been peeing or pooping in the house for the first 3 weeks and now every morning I wake up there is at least one spot where he has peed or pooped.

He goes at night when I am asleep. I take him out for a pee in the morning as soon as I get up, a really long walk after dinner, and out in the front yard before bed. I have been rewarding him treats every time he does his business outside. Am I doing something wrong?

By Maddy. S