If the problem is centered on your computer, browser or network hardware that you own then it is on topic at Super User.
If the problem is that your ISP has problems then it is very much on the cusp. We have no control of ISP hardware and at best would suggest working around it with something like a VPN.
If the problem is that the website is unreliable and everyone is getting this error then it would be off topic as we have no control over their hardware, software or errors.
It's a bit of a "chicken or egg" situation to do the fault-finding necessary to establish where the problem is though.
- If you get the problem only on one machine then that points to that machine having a problem. Could well be on topic - you might have some "internet protection" suite or extensions in your browser causing it.
- If it happens to every machine on your network, but never on a machine on a different network then that points at your network or ISP. Might be that you just need to reboot the router to fix, or it might be a wider problem with your ISP.
- If it happens everywhere for everyone, then that is a website problem and is almost certainly off topic.
The line between on and off-topic is slightly blurry, hence it can help if you provide all the information on when, where and what actually happens. It can also be worthwhile telling us when it does and does not happen.