I think I have an idea.
You ran the quiz data upgrade tool when you weren’t supposed to. Because of this, your quiz settings got scrambled/corrupt, which is causing the quiz settings page to not fully load.
The data upgrade tool states
This tool is only needed for users upgrading from HD Quiz 1.7 or lower.
But I’ll amend it for the next version of HD Quiz to also give an extra warning to NOT run the tool if already on 1.8x. Hopefully that will discourage anyone else in your situation from making this mistake and save someone from the same issue in the future.
Something to try that will A) get this fixed for you (although in a roundabout way), and B) prove my theory.
Create a new quiz, and set the quiz settings to whatever you want, and save.
Did it save OK? If the new quiz settings save OK, then this pretty much confirms that the issue is that your old quiz settings are corrupt which is what is causing the issue. You can then use the “BULK MODIFY QUESTIONS” to add your existing questions to the new quiz, and delete the old quizzes once done.
Please let me know if the above works and let me know how many quizzes / questions you’d need to do this with.