Occassionally when members view their MySQL based sites (especially forums),
they occassionally get 502 poxy error.

It states:

Proxy Error

The proxy server received an invalid response from an upstream server.
The proxy server could not handle the request GET

Reason: Error reading from remote server

Obviously the GET path is different based on path or account.

In order to get rid of the problem they have to refresh like 1-5 times until it
displays the right page.

Can you please let me know why this is happening and what to do to fix it?