At the end of the movie, and even during Little Homeschool, Steven seemed to have moved on from his mommy issues. He had learned that he wasn't responsible for her actions, so all he could do was to take on her positive traits of kindness and forgiveness and pay it forward. Suddenly in Volleyball, he starts having massive mommy issues again after hearing about one more bad thing she did. He's also got some personal issues with the gems for no good reason. The conflict doesn't seem like it fits because there was no buildup to these issues in the original series. These problems were amorphous until Volleyball and now they've progressed into creating literal monsters like Cactus Steven.