Update Regressions 2 stories

Update Regressions belongs under Troubleshooting & Failure Modes because its symptom, causes, and verification steps depend on that technical context. The diagnostic focus is new faults that appear after an otherwise successful update, with attention to changed drivers, settings, APIs, performance, compatibility, rollback options, and evidence that links the regression to the change. A good diagnosis distinguishes the failing layer from similar symptoms, favors reversible checks first, and ends with validation rather than assuming one successful attempt proves the issue is solved.