Why are my manual YouTube video chapters missing when my timestamps meet the rules?

If the timestamps are already formatted right, the next thing to check is feature access. YouTube lists chapters as an Advanced feature, so open YouTube Studio on a computer and check Settings > Channel > Feature eligibility. For the description itself, YouTube still requires 00:00 as the first entry, at least three timestamps in ascending order, and every chapter to run at least 10 seconds. Also make sure you edited the video description itself and hit Save; adding manual chapters overrides automatic ones. If Advanced features are enabled and that exact setup still doesn't show after the saved description is live, YouTube's help page doesn't give a more specific manual-chapter diagnosis, so I'd use Studio's feedback option rather than keep changing compliant timestamps.