It'll not be the same problem, but it's likely related. It occurs when the back end server is under high load and so the front end cache server is timing out waiting for a response.

I realise this can be very annoying, for which I apologise. I'll have a look into it to see if there are some performance problems I can spot.

It ususally happens most when the site is attacked by spammers who send thousands of requests to try to log in or post things as different fake users. These are generally harmless because they get blocked, but it does increase server load while it occurs.

Thanks

Joe