What does this mean?
This indicates that the page is using both a service name in the GOV.UK header as well as a service navigation component, similar to in the screenshot below:
The service navigation component is a replacement for the service name presence in the GOV.UK header, so the two should not be used together.
Impact on users
The impact on users is primarily the repetition having the service name in both places causes.
How to fix
Remove the service name from the GOV.UK header, leaving it just in the service navigation as in the screenshot below:
Check the service name in the service navigation matches that in the page's title element.