The situation described in the question indicates that there are multiple problems in the Scrum Team that have led to the increase of technical debt and the dissatisfaction of the Product Owner.These problems include:

The Scrum Team has not used the past Sprint Retrospectives effectively to inspect and adapt. The Sprint Retrospective is an opportunity for the Scrum Team to reflect on their performance and identify improvements for the next Sprint. If the Scrum Team has not been using this event properly, they may have missed some issues or opportunities that could have improved their quality and value delivery.

The Developers have not been paying enough attention to quality. The Developers are accountable for creating a potentially releasable product increment that meets the Definition of Done and the Sprint Goal. If the Developers have not been focusing on quality, they may have introduced defects, errors, or inefficiencies that compromise the functionality and usability of the product.

The Scrum Team is not having conversations around technical debt. Technical debt is the accumulation of work that needs to be done to ensure that a product is maintainable and extensible in the future. If the Scrum Team is not discussing and managing technical debt, they may be neglecting some important aspects of the product architecture, design, or code that could affect its scalability, performance, or security.

The Scrum Master has not ensured that the Scrum Team is being transparent. The Scrum Master is responsible for establishing an environment where transparency, inspection, and adaptation can occur. If the Scrum Master has not ensured that theScrum Team is being transparent, they may have allowed some hidden problems or assumptions to persist that could affect the quality and value of the product.

References:

Scrum Guide 2020, page 13: “The purpose of the Sprint Retrospective is to plan ways to increase quality and effectiveness.”

Scrum Guide 2020, page 10: “The Developers are the people in the Scrum Team that are committed to creating any aspect of a usable Increment each Sprint.”

Professional Scrum Master II Course, page 12: “Technical debt is a metaphor for expressing how doing things in a suboptimal way can accumulate over time and make it harder to change or improve a product in the future.”

Scrum Guide 2020, page 6: “The Scrum Master is accountable for establishing Scrum as defined in the Scrum Guide. They do this by helping everyone understand Scrum theory and practice, both within the Scrum Team and the organization.”