There's a known problem that affects receiving achievements for quizzes, being able to mark answers correct and highlight incorrect answers for quizzes, attempting to download ebooks and discovering that the form to do so is blank, or claims that you need to re-register for an account, or re-login, and similar when applying for a Design Challenge or RoadTest.
The issue appears to be related to caching and presenting JavaScript to the user. The admin/dev ops team are having difficulty repeatedly recreating this scenario to narrow it down, however, we're aware that members are experiencing this issue repeatedly.
You may be able to work around this by clearing your browser cache, using a private tab, incognito mode, changing web browsers, and making sure that you're not blocking JavaScript.
The development team has been aware of this issue since at least July 2023 and is still looking into it.