What is the CV check?
It reads your CV the way an applicant tracking system does, against a rulebook you can read, and points out what could trip it up. Only you see it.
It looks at contact details, sections, dates, wording and length, and at problems you cannot see by eye, such as letter pairs that a PDF font has swallowed, so a program reads a word wrong.
You see the result before you send an application, and each application under My applications shows the check it got.
No employer sees the check or its result.