I still think it's the proxy's waiting time for the server.

Ir is not , because it was working fine like 3 days ago.

Server response time is the same

Could the forum be causing the errors? Perhaps it's time to tag @theymos in the discussion and see if he has any ideas.

It is possible that he changed something in the server recently, which may be blocking too many requests....

Nothing should have been changed:

Yeah, now the imageproxy is under a DDoS. (You may still see some images due to caching in your browser.)

I'm not going to try to fix this.

This is probably the cause.