Hello,
I’m unable to edit files but I have done the second option.
I changed my theme to the twenty-twenty theme and deactivated all plugins at the same time except HD Quiz and it is still having the same issue.
P.S: I have another website that uses the same themes and plugins as this “troubled” one & I have previously installed HD Quiz on the former website and it is working fine, I don’t know why this other one is proving difficult. Sigh!