PMP Practice: Monitor and validate scope

Sky Tanaka is leading an agile project for Bright Pulse Labs to develop a mobile puzzle game with a planned six-sprint release cycle. At the end of Sprint 3, the product owner realizes that the team has delivered 18 user stories totaling 72 story points, but only 9 of those stories align with the features customers actually requested during recent user testing sessions. The other 9 stories were technical enhancements the development team prioritized on their own. The product backlog still contains 45 high-priority user stories requested by stakeholders, and the team's average velocity is 24 story points per sprint. The product owner is frustrated that customer-facing features are falling behind while technical work was completed without their approval. What should Sky do to get the project back on track?