Howard Miller

You can tell if they've clicked on it. You can only tell if somebody has actually watched a video if you ask them questions about it. Moodle can't look inside their brains.

Have you noticed the comments? The AI generated code is looking for you to complete some of the functions.

This is why you need somebody who knows what they are doing (not AI)

I'm not sure why you think NFS is not recommended. NFS is fine. However, don't rely on it for anything performance critical. This is likely to come down to the Moodle Cache. Implement a Redis server for that and you should be fine.

I'm not sure I can answer that. Did you install Moodle (if not, who did)? Do you have access to the server/hosting it's running on (if not, who does)? If you do have access, do you know much about it?

Another complete guess - you're running some old version of Moodle and whoever hosts it has routinely upgraded the underlying server resulting in incompatible versions. It'll be something like that. Depending on how ancient your Moodle is, you might be in for a bad time fixing this. 

On the face of it, the issue lies with https://moodle.org/plugins/mod_studentquiz

An optional module that I must admit that I have never heard of. Possibly worth raising a bug report over there.