Examples:

1. Zuko betraying Iroh (ATLA) - Zuko went through a full fever dream where he had to let go of his desire for Honor, but when tempted by his sister, he immediately betrays Iroh and goes after Aang. Which helps make his redemption arc better, as the rest of his story involves him fitting in with Team Avatar and reuniting with Iroh. 

2. Rigby goes to China (Regular Show) - Rigby wants to improve himself, and so he goes back to high school, but he needs to pass a language class. So he hijacks Benson's trip to teach students in China, where he causes disturbances in the class and mocks Benson. Benson confronts Rigby on this, saying that while he wants to change, Rigby has never changed. I think it works cause there's a difference between saying "I want to change" and actually changing. Rigby proves he truly can change. 

3. Angel Dust drinking with his friends (Hazbin Hotel) - Angel throughout the series went through massive evolution, slowly distancing himself from just a horny twink to trying to maintain decent friendships and keeping himself stable even with all the pain and trauma. In one episode, Angel was brutally overworked by Valentino, so Cherri Bomb decided to come by and give her friend a night off, which included Angel's friends as well. In the nightclub, Angel hesitates about drinking cause it goes against his rehabilitation; however, since he had a rough day, he chooses to drink. It works out here because it makes the rest of the series even better as Angel is put in a situation where he has to stand up for his friends against his abuser, which proves to Charlie and Heaven that he truly did change. 

When a character slightly regresses in their redemption arc (which makes the redemption better)