According to the PMBOK® Guide, specifically the Monitor Risks and Implement Risk Responses processes, a project manager must follow the established risk management plan when an identified risk triggers.

Risk Realization: In this scenario, the " risk " of late delivery due to poor quality has materialized into an Issue. However, PMI methodology dictates that if a risk was previously identified and documented, the first step is to refer to the Risk Register to execute the pre-defined Contingency Plan or Risk Response.

Cohesion with Quality Management: The issue involves User Acceptance Testing (UAT) and Severity 1 (S1) defects. These are critical blockers. The Risk Register should ideally contain responses for " Quality Issues " or " UAT Delays, " which might include re-allocating senior resources, utilizing specific testing tools, or adjusting the schedule based on a pre-approved buffer.

Structured Management: By implementing established risk response actions, the project manager ensures that the solution is handled systematically rather than through " knee-jerk " reactions. This maintains the integrity of the project ' s governance and ensures that the response is one that stakeholders have already agreed to in principle.

Analysis of other options:

Option A: Creating a new risk for each defect is redundant and reactive. The risk (late delivery due to quality) is already known. Individual defects are issues to be tracked in a Defect/Issue Log, not a Risk Register.

Option C: Asking developers to work longer hours is a form of Crashing. This is a last-resort schedule compression technique that often leads to lower quality and more defects due to burnout. It should not be the first step without consulting the plan.

Option D: Attempting to find a different person to sign off on UAT to bypass the Product Owner is a violation of project governance. The Product Owner is the authority on value and quality; bypassing them undermines the project ' s success and the Stakeholder Engagement Plan.

Per PMI standards, the most professional and effective action when a project hits a known roadblock is to Consult the Risk Register and act upon the strategies that were developed during the planning phase to handle exactly this type of situation.