For a couple of days, it has not been possible to see a match quiz in preview. When I click the link, either in my own quiz or in one which I am editing, I get the following message:
An Unexpected Error has Occurred
We are unable to continue because an error has occurred.
The administrators have been notified of the problem.
Please hit back on your browser to continue.
It is useful for authors to see that screen, as it sometimes alerts them to a display issue (maybe a question runs over to an extra line) that they can correct when they see it, but which is not obvious in the edit quiz mode.
I thought it might be a temporary glitch because something was in the process of being changed, but it has been around for a while.