Coparenting advice needed!!

My ex and I separated a couple years ago and split custody of our son 50/50. Over the summer, she was working retail and couldn't keep him most of her days. I wound up with kiddo 5 days of her week, every week. My mother watched him during the day while I worked. My mother and I are on the same page when it comes to rules, behavior, and expectations. The ex is.. .chaotic. Rules and consequences constantly shift at her house. She lets him do whatever he wants until she can't stand it and then she starts screaming and yelling. After she gets that out, things go back to what they were before the explosion as if she never said anything. With my mother and myself, we stop unacceptable behavior immediately and punishments are typically taking away TV or privileges. We use time-outs a lot.At the start of this school year, he was doing amazingly well with behavior. At the same time, the ex got a better job and could keep him all her custody week. As time has gone on, his behavior at school has declined. He is hitting other kids constantly. It's not with fists, but with papers or straws. His respect for personal boundaries has broken down. It's been a problem in the past, but we worked hard on it all summer and he was doing well. At his mom's house, he is constantly climbing all over her, poking her with toys, and doesn't stop even when she tells him "No".So, I'm at a loss. The ex claims she isn't letting him misbehave, but that's obviously not the case. As soon as he sees her, he stops following any rules. Of I tell him to stop, he tells me "my mama let's me do that, so it's ok." If I'm there, I intervene, but I cant be there all the time and she gets very resentful and belligerent when I step in around her.Toward the end of my weeks, he starts doing better, but after she's had him, he is a real handful. Kiddo is 7 and he's learned quickly to play mom against me. She wont hear anything I bring up about it. She just insists it's not real and I'm just trying to make her out to he a bad parent. She's not a bad parent, but her lack of consistency with kiddo is taking its toll.I could really use some guidance or experiences from other people who dealt with similar situations. Sitting kiddo down and talking reasonably doesn't work. Taking away privileges doesn't work. I'm at my wits' end. via /r/Parenting https://ift.tt/2Sxz5fE