Did you try other browser? I have never come across this in my btctalk lifetime.
This not a browser problem. I heard it happened to a few more people.
In my experience I think this is happen due to a weak server. But I want the opinion of more experts
No. In my experience, it has nothing to do with
a weak server, as you say. If that were the case, we'd all be getting 500 Internal Server Errors.
This is simply the result of a server's DDoS protection that kicks in when there are too many inbound requests in a very short time frame.