PMP Practice: Execute quality management plan

Ash Okonkwo is the agile project manager for Polite Explosion Studios, an indie studio developing a narrative-driven mobile game. After three sprints, the product owner is frustrated because multiple user stories marked 'done' have significant defects when integrated into the main build. Players in beta testing report that dialogue choices don't trigger the intended story branches, and character animations freeze during critical scenes. The development team insists they completed all acceptance criteria before marking stories done. The product owner argues the acceptance criteria were too vague and didn't capture the necessary quality expectations. Sprint reviews have been attended by the team and product owner, but technical debt has accumulated, and the team is now spending 40% of each sprint fixing issues from previous sprints rather than delivering new features. What should Ash have done earlier to prevent this quality gap?