Hello,
I've read your requirements very carefully. I'm sharing some issues/ideas will help you to identify the root cause. It's all about the experience of troubleshooting, nothing else. It's a complete logical work. Look, as you can access the offline contents with satisfaction speed means is that, there is nothing to do with the contents.
There is something you need to do with traffic flow. Here two/three layers need to do some work which will help you fix this issues.
As I'm in this industry and doing the same work over the last 15 years, I can assume to see or hear the incidents.
To have a look of your problem, It's related with network/traffic issue, nothing else.
Please knock for further process. I'll fix this issue within very short time applying two more ways which will help your students to get the access of your offline contents as like as you.
Regards,
Sanjit