What does this mean?
This indicates a link is missing the govuk-link css class which adds the high contrast link focus styles.
Turning off this check
It might be that you are reviewing a service which is implementing its own link styles and this issue does not apply. In this case to reduce noise when running the plugin you can disable this check by deselecting the “Check focus” option in settings.
Impact on users
Without the css class the link will only receive the standard browser focus styles which vary between browsers but which are generally very poor. This can make it difficult for users to identify the location of their focus when using a keyboard.
How to fix
Make sure the link has the class assigned.
For example:
<a href="..." class="govuk-link">Continue</a>