This is advice, not conformance
No WCAG success criterion requires this check, so failing it does not fail an audit. It still catches real problems, which is why we surface it — separately, so your compliance score stays honest.
How it is reported
A11ySignal reports this at moderate impact. Every failing element comes with its CSS selector and the markup that failed, so you can go straight to the line rather than hunting for it. Deque publishes the engine-level detail:
https://dequeuniversity.com/rules/axe/4.13/landmark-no-duplicate-banner ↗
Check implemented by axe-core 4.13.0, © Deque Systems, MPL-2.0.