It was possibly a glitch, but not with HD Quiz.
The “glitch” would likely be a temporary one with your caching plugin.
Caching plugins are extremely complex. My best guess on what happened is that you were looking at the site while the cache plugin was minifying or combining assets (CSS, JS files, etc). Since you were logged in, you’d be seeing the “dynamic” site instead of the “static” site that actual users will see. Once the plugin finished doing its thing, you were able to see the site perfectly again.
Another possibility is that it could have been a temporary glitch or server hangup where your connection was stopped before the full site could load. HD Quiz loads assets in your theme footer so that HD Quiz never slows your site down. If the server connection failure happened before your footer could load, or a fatal error caused by your theme or another plugin happened, you’d see the questions and stuff but would not see the styling or functionality.
It could even be local a browser cache glitch – meaning your browser temporarily messed up and corrupted its cache, and simply refreshing the page/clearing your local cache would fix the issue.
Basically, there are many reasons this could have happened, none actually related to HD Quiz. The good news is that it’s almost certainly a rare and temporary glitch.
If you see it happen again, try changing cache plugins (I personally love WP Fastest Cache), or even contact your host if the issue ends up being server timeouts.
Hope this makes sense. Modern servers and the internet can be an interesting beast.