I think the problem may be with your browser or extensions used. Try another browser or disable any extension that you think may be the problem as the Note at the beginning of the course says:
Note: Some browser extensions, such as ad-blockers and dark mode extensions can interfere with the tests. If you face issues, we recommend disabling extensions that modify the content or layout of pages, while taking the course.
As that was the same problem similar to yours here: FCC forum