When user tries to enter a quiz a bit too late, it shows the reason within error message.
That message shows html-code amidst the plain text.
 

"You are not allowed to attempt this quiz at this time because: <p class="text-left">This quiz is currently not available.</p>"

More information about this error"

A way to reproduce the error

1. As admin/teacher create a quiz with at least one question
2. Go quiz setting 'Set Timing' > 'Close the quiz' e.g. after 1-5 minutes in the future (which ever time it takes to open the quiz as student)
3. Log in as a student account
4. Go to the course and click to open the quiz, but do not Attempt quiz yet.
5. Wait until the quiz closing time goes over
6. Push "Attempt quiz" button to try to start the quiz -> error is shown